How Do Sleep Trackers Work And Are They Reliable Enough?

photo of me wearing a sleep tracker in bed

You spend around a third of your life asleep, with the amount and quality of sleep having a huge impact on the rest of your life.

So it’s natural to be curious about how long you really sleep for, and whether you’re getting enough good quality sleep without any sleep disorders to address.

Until just a few years ago, your options for assessing your sleep were somewhat limited: you could keep a sleep diary if you had the dedication; ask your partner about your sleep; or record yourself sleeping (an unlikely activity!)

The only way to accurately assess your sleep would be to spend a night or two in a specialist sleep clinic. But now there’s another option to improve your accuracy of self-assessment: the personal sleep tracker.

A question of accuracy

How do consumer sleep trackers work though? How do they compare to the equipment and expertise in a sleep lab? And can you actually rely on the information they provide?

These are important questions to consider, especially if you’re thinking of spending a fair bit of money on one.

I’ve been conducting a sleep tracker review for several years, regularly testing new wearable and non-wearable devices. And what I’ve come to realize is that there’s quite a range in terms of what they measure, and how they do it.

So I decided to investigate what researchers have to say about the accuracy of both the devices themselves and the technology behind them.

Hopefully, this article will give you a better understanding of what you can expect from your sleep tracker. And how much you can trust all the information about your sleep they claim to provide.

How sleep specialists measure sleep

man undergoing polysomnogram

To understand the strengths and weaknesses of personal sleep trackers, it’s useful to first take a look at how specialist sleep centers measure sleep.

If your doctor suspects you have a sleep disorder, they might refer you to a sleep clinic for a sleep study, also known as polysomnography.

This typically takes place over a night or two, with different pieces of equipment measuring your sleep stages and cycles. Someone will usually observe you while you sleep as well, and so a lot of information is gathered about your sleep, including:

  • Brain waves.
  • Breathing.
  • Heart rate.
  • Body movement.
  • Leg movement.
  • Eye movement.
  • Blood oxygen levels.
  • The positions you sleep in during the night.

All of this information is then used by sleep specialists to assess your sleep and diagnose any sleep disorders. This detailed analysis and use of brain wave monitoring is why polysomnography is often referred to as the gold standard of sleep assessment.

Sleep trackers Vs polysomnogram

Logically, it’s hard to imagine how a small sleep tracker worn on the wrist, a strip placed under your mattress, or even a smartphone App could do the same as all these high-tech measuring devices. A major difference is that consumer sleep trackers don’t measure brain waves, which is a key way a polysomnogram determines sleep stages.

So I think it’s useful to bear this in mind when it comes to the expectations you might have of your personal sleep tracker. It also leads to an important question: if personal sleep trackers can’t measure all of those factors, what exactly can they reliably do?

As you’ll see later, some of them are reasonably good at measuring basic sleep information, such as the total time you spend asleep and how often you wake up in the night. To understand what they can actually do though, let’s first take a look at the technology inside the trackers.

The science behind wearable sleep trackers

One of the key measuring tools of wearable sleep monitors is called actigraphy. Actigraphy essentially involves recording movement through a measuring device called an accelerometer.

The idea is that a certain amount of movement corresponds with being awake, and periods of being still indicates that you’re asleep.

As Fitbit says on their help page:

When you haven’t moved for about an hour, your device assumes that you’re asleep. Additional data—such as the length of time your movements are indicative of sleep behavior (such as rolling over)—help confirm that you’re asleep.

Why actigraphy can be useful

Actigraphy has been used by sleep clinicians for decades to measure sleep. Even though polysomnography is the gold standard for sleep measurement, actigraphy also plays an important role, especially as polysomnography isn’t without its own issues.

When a patient is hooked up to various machines with multiple electrodes stuck to their head, and in a lab rather than their own bed, they understandably might not sleep normally.

So not only is actigraphy less expensive than polysomnography, but people can wear a device in their own home for a week or two, giving a more natural insight into their sleep than just one or two nights in a clinic.

But how accurate is wrist actigraphy, and what can it accurately tell you about your sleep?

Fortunately, there’s been a fair bit of research into those two questions.

How accurate is wrist actigraphy?

In 2011, Martin and Hakim published some fascinating research into the usefulness of clinical wrist actigraphy. Importantly, they looked at how actigraphy compares to key forms of sleep assessment:

  • Clinical interviews and sleep questionnaires.
  • Daily sleep diaries.
  • Laboratory Polysomnography.
  • Videosomnography in children.

They state that wrist actigraphy is useful for assessing sleep in a natural environment, rather than in a laboratory setting. However, they do advise caution against relying on it solely:

Although actigraphy should not be viewed as a substitute for clinical interviews, sleep diaries, or overnight polysomnography when indicated, it can provide useful information about sleep in the natural sleep environment and/or when extended monitoring is clinically indicated.

They claim that wrist actigraphy can be quite accurate when it comes to estimating information such as total time asleep, sleep percentage, and how long after sleep waking occurs.

However, they also state that the main limitation is mistaking being awake and motionless for being asleep. This could then make it difficult for those who wake many times, or with severe insomnia, and who tend to lie still in bed awake rather than move about.

This is also one of the key points which consumers complain about with commercial sleep trackers. Looking at online customer reviews, for example, will turn up many complaints that time lying in bed watching television or reading a book was recorded as being asleep.

Comparing two types of assessment

In 2013, researchers in the United States also looked into the accuracy of wrist actigraphy compared to polysomnography. They found very similar results to the 2011 research:

…we conclude that wrist actigraphy with current algorithms is of value for individual-level estimates of both sleep duration and wakefulness after sleep onset

They also mention the idea that results from actigraphy might help people get an objective measure of their sleep, especially when having treatment for insomnia, for example. Considering many people tend to underestimate how long they sleep for, this could help them see that the treatment is in fact helping.

The limitations of actigraphy

A point I’ve seen made in many online articles where sleep experts have been contacted by the writer is that sleep trackers perform better when you sleep reasonably well.

It’s when you have a disrupted night’s sleep that errors become more apparent. And it seems it’s not just the skeptical owners of sleep labs that think this – there’s research to back it up.

Sleep trackers perform better when you sleep reasonably well. It’s when you have a disrupted night’s sleep that errors become more apparent.

Study 1

A study by Terri Blackwell in 2008 compared actigraphy with polysomnography in older women. She cautions that the more disrupted the sleep, the less accurate the sleep tracking. However, she did find that actigraphy is reasonably accurate for people to use in their homes:

Actigraphy does not replace polysomnography in sleep estimation, but was a convenient, affordable and accurate method of collecting measurements of sleep in a large epidemiologic study of older women…Sleep parameters from actigraphy corresponded reasonably well to PSG in this population…Those with poor sleep quality had the largest measurement error between the 2 procedures.

Study 2

A team of Korean researchers in 2018 compared the sleep diaries of 78 people over 14 nights with several sleep trackers:

  • ActiGraph GT9X Link
  • SenseWear Mini armband
  • Basis Peak Fitbit Charge HR
  • Jawbone UP3
  • Garmin Vivosmart

Even though some of these are now old models or discontinued, some of their findings are still interesting:

Overall, we found that the SenseWear, Fitbit Charge HR, Jawbone UP3, and Garmin Vivosmart can be valid measures of TST (Total Sleep Timre) and TIB (Time In Bed) when compared with a sleep diary in a healthy adult population in a free-living setting. However, these trackers cannot be considered valid regarding wake times during a night of sleep…our study also found greater discrepancies between reported variables during nights that appeared to consist of more disrupted sleep (i.e., the sleep diary reported 7 h of sleep and each band would report between 2 and 7 h of sleep for that night).

So it seems that although wrist actigraphy can be useful for some measurements, it struggles in certain circumstances. And frustratingly, it seems they struggle most when you’re not sleeping well – which is in theory when many people would appreciate some accuracy!

Manufacturers aware of the issue

Manufacturers of sleep trackers are aware of these limitations. In response, some devices allow you to manually override the automatic sleep tracking – either to say exactly when you’re trying to sleep rather than relax in bed, or to correct errors in the morning.

But let’s face it – if you have to keep doing this, your faith in your device is going to plummet.

Beyond actigraphy: heart rate and respiration in consumer sleep trackers

When I first started reviewing sleep trackers, actigraphy was all there was. But now, some include other measures, such as heart rate, heart rate variability, and respiration to help improve their estimations of your sleep.

To make matters more complicated, sleep trackers seem to have branched off into two major types, within which there are subtypes (as I call them):

  • Wearables: most are worn on your wrist, and also function as activity trackers and/or smartwatches. Some recent devices are worn on the head.
  • Non-wearables: Measuring strips that sit under your mattress and work by ballistocardiography, tracking small movements made as your heart pumps blood and you breathe. Or a device that sits on your nightstand and measures points like breathing, movement, light and noise. One or two that clip onto a pillow. Some smartphone Apps also try to track sleep.
beautyrest and emfit qs sleep trackers
The BeautyRest and Emfit QS that I had under my mattress at the same time when I tested them side by side in 2018

Going back to the Fitbit help page, which also explains how they now track sleep stages, they summarize how they ‘estimate’ them.

And this is a key point: sleep trackers don’t exactly measure your sleep, but they estimate it based on data they collect and algorithms the manufacturer creates:

While you’re sleeping, your device tracks the beat-to-beat changes in your heart rate, known as heart rate variability (HRV), which fluctuate as you transition between light sleep, deep sleep, and REM sleep stages. When you sync your device in the morning, we use your movement and heart rate patterns to estimate your sleep cycles from the previous night. 

Sleep stage tracking: the unmeasurable elephant in the room

Estimating your sleep based on a combination of actigraphy, heart rate or breathing is great (when it works), and my feeling is that it will get better in time as technology improves.

However, along with the inclusion of new measuring tools arrived a giant elephant in the room: sleep stages.

photo of an elephant in a room

Whether sleep tracker manufacturers decided around the same time that the technology was good enough to offer sleep stage data to users, or they were worried about not selling if they don’t offer what competitors do isn’t for me to say.

But here’s the problem: unless you have access to a sleep lab and brain wave measuring, you have absolutely no way of knowing if your sleep stage data is accurate.

So we have a situation where some consumers don’t even worry about it and trust the way their expensive new toy works, while others have suspicions but no way to confirm them.

And neither of those is ideal.

Sleep researchers compare sleep trackers with polysomnograms

I suspect many people would like to know how big the elephant in the room is, but we just don’t own elephant measuring tools. And there’s no authority that regulates sleep trackers to help us out.

However, there have been a handful of studies in recent years where sleep researchers have compared sleep trackers with polysomnograms, EEG or sleep diaries.

The problem, as I see it, is that manufacturers regularly release new models or update the firmware. So most available published research involves sleep trackers that are either older models or entire brands that have since discontinued (such as Jawbone).

Still, they are interesting to consider as there are some common findings that crop up more than once.

photo of 3 sleep trackers on one arm
Three of my old sleep trackers, still available but slowly being pushed into history by newer models arriving

1. Portable EEG + Fitbit Versa (older model)

A study in 2019 particularly interested me as it involved one of my favorite wearables – the Fitbit Versa (even though the Versa 2 is now out).

20 people used the Versa for 14 nights, as well as a portable EEG. They found the Versa was similar to the EEG for total sleep time, time in bed and calculated sleep efficiency. However, it differed when it came to sleep stages, time to fall asleep and time of first waking. They concluded:

The consumer sleep tracker could be a useful tool for measuring sleep duration in longitudinal epidemiologic naturalistic studies albeit with some limitations in specificity.

2. Polysomnogram + Jawbone UP3 (now discontinued)

Even though the Jawbone UP3 is now discontinued, this 2017 study is interesting because 17 patients wore the UP3 while undergoing a polysomnogram in a sleep lab.

The results weren’t the best for Jawbone though. They found it significantly overestimated total sleep time and sleep efficiency. And it was found to overestimate REM latency, total REM sleep time and deep sleep time. And it underestimated the time to fall asleep and time of first waking.

The grim conclusion was:

The JB3 inaccurately estimated sleep duration and efficiency relative to PSG. Further investigation to determine JB3 specificity, sensitivity, and accuracy for sleep staging, as well as the evaluation of the JB3 to measure sleep during naps, is warranted.

And considering the lack of studies like this done for any sleep trackers, it didn’t inspire much confidence in general!

3. Polysomnogram + Jawbone

Just to be fair to Jawbone, especially since we’re all hoping for a resurgence in the future, there was an interesting study in 2015 of the Jawbone UP before sleep stages came along. The results were more positive than the previous study, as the authors say:

Jawbone UP shows good agreement with polysomnography in measures of total sleep time and wake after sleep onset in adolescent boys and girls.

4. Polysomnogram + Bodymedia SenseWear Pro Armband (medical actigraphy) + Withings pulse 02 + Jawbone Up

This study compared two commercial trackers – the Withings Pulse 02 and Jawbone UP with PSG with medical lab sleep tests, specifically with 36 obstructive sleep apnea patients.

They again found mixed results with the only positives being that they correctly assessed time in bed and light sleep. But no other measures were deemed to be accurate.

5. Polysomnogram + Actiwatch-64 (medical actigraphy) + Fitbit

This study, done in 2012, is now pretty old and Fitbit has made significant changes to its sleep tracking. However, since highlighting Jawbone’s problems, it seems only fair to bring this one up.

Interestingly, despite being caught out by the polysomnogram, it was at least no worse than the medical grade actigraphy, as noted by the authors:

Fitbit has the same specificity limitations as actigraphy; both devices consistently misidentify wake as sleep and thus overestimate both sleep time and quality

6. EEG + Fitbit Charge 2 (older model)

If heart rate changes are used when estimating sleep, surely that’s an easier one to check – especially during exercise.

The Charge 3 is now the latest version, but nevertheless, a study in 2018 found some worrying results while recording the heart rate of 15 participants riding a stationary bike.

Compared to an electrocardiograph, they found that while it wasn’t too far off in some cases, there were incidences where the error was large:

Whilst there is only moderate bias on average, precision is poor for individual measurements, which could plausibly be underestimated by as much as 30 bpm.

To be fair, the authors do note that the way the device is worn on the wrist can lead to errors. And this, presumably, can also happen during sleep:

…instability and improper positioning of the device may potentially explain different results and poor-quality HR data.

7. My own tests in 2018

In 2018, I tested 3 different sleep trackers at the same time, comparing them to my manual sleep diary. I didn’t compare them with an objective polysomnogram, but I thought the results were interesting nonetheless.

One standout result was that the sleep stage reporting of all three was wildly different. So that ruled out the admittedly small chance that they were all accurate!

And with other points I could measure myself, like estimated time of falling asleep and time of waking, I found the Versa and Beautyrest were ‘reasonably’ accurate, while the Emfit struggled.

And that raises another point: where do we draw the line where accuracy is concerned? One person’s definition of ‘reasonable’ could be another’s motive to log into eBay.


The results of the studies above aren’t exactly reassuring – to put it mildly.

As I said though, technology advances quickly, and to my knowledge, there are no published independent studies of the latest devices made by the companies which have been put to the sword. And there are a few brave new companies entering this lucrative, yet vulnerable to self-destruction, market.

So what can you take from all of this?

Well, my personal take remains the same as it did when I first wrote about sleep trackers six years ago: take the results with a pinch of salt, and don’t get too caught up in the finer details of the sleep tracking data – especially where sleep stages are concerned.

I think it’s good to have realistic expectations of what you can get from your sleep tracker. They are potentially a useful tool for giving you an overview of your sleep. Just be aware that they aren’t perfect yet, and will make mistakes from time to time.

It’s still a developing technology, and it will be very interesting to see just how accurate they get in the coming years.

For now though, if you have sleep problems, remember to speak to your doctor/physician about it.

At the end of the day, they and the sleep specialists they can refer you to are still the most reliable way to find out about your sleep and diagnose any sleep disorders.

Your views

What do you hope to find out from using a sleep tracker? Which device have you tried before, and did you find it to be accurate, or provide you with useful information?


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    • Hi Mylinh
      Could you tell me where you got the information from that they are one of the best sleep tracker, and which ones specifically as there are more than one.

  1. Hi! Thank you for the article!
    My name is Heather, I am diagnosed with Type 1 Narcolepsy… so, tracking my sleep is more than just something of interest for me. I did LOADS of research about tracking devices before buying one. Non-wearables aren’t an option for me, because I can literally fall asleep anywhere at just about any time.
    So, I needed a device that would automatically detect and record my sleep at any time of day.
    I ended up buying an Honor Band 5. It’s been really amazing at detecting the difference between awake and still vs actually sleeping, even if I only fall asleep for ten minutes, it picks it up and records it as a nap. Any amount of time less than 3 hours is recorded as a nap, and it doesn’t give sleep architecture data for that. However, for periods over three hours, it has 3 different levels of sleep and shows when you wake up, too. Light sleep, deep sleep, REM sleep, and awake. It graphs it out in an easy to read way, and then gives percentage data underneath the graph. It so shows breathing quality, and “deep sleep continuity” . It averages my sleep by day, week, month, and even year. Clearly, I don’t know how accurate the levels of sleep being shown are, but I can tell you it almost never misses it when I am awake. I have a 2 year old son, so in addition to my own terrible sleep at night, I have a baby waking me up, and the read out shows pretty accurately how many times I wake up.
    It also measures my heart rate, and my blood oxygen levels, which I think helps it track my sleep more accurately.
    This fitness tracker has lots of great features; it controls my music on my phone, measures nearly every kind of exercise, including swimming, it’s waterproof, does normal things like step count and displays texts and incoming calls, and helps me find my phone when I lose it.
    The only downside is that it doesn’t have very many faces to display, and it won’t connect to any third party apps. It only works with Huawei Health. But you can choose which apps you get notifications from, so if your Gmail is constantly blowing up your wrist, you just turn off the notification.
    The battery life is fairly good. I have mine on constant heart rate monitoring and I have tru sleep enabled so that uses my battery a bit faster. I usually have to charge it every 3 or 4 days, or I take it off to charge while I’m in the shower everyday and that keeps it charged.
    When I bought mine last November from Amazon, it was less than $40… which is a large part of the reason I decided to give it a chance. I figured if I hated it, I could return it, and $40 isn’t that much money to gamble with, unlike a $200 or $300 brand-name smart watch…
    All in all, I am really satisfied with my Honor Band 5 and I definitely recommend it!

    Has anyone else tried this watch? I’d love to hear about anyone else’s experience with it…

    • Hi Heather
      I haven’t tried it myself, but it was interesting to read your description of it, so thank you for sharing that!

    • Yes Heather this Honor Band 5 looks amazingly good with very good accuracy. I wonder how it detects different sleep levels, is it just detecting heart rate and body movements and then determine the level of sleep. what other body parameters does it consider. How can we validate the accuracy of the device.

    • Hi Ron

      I have the Dreem band and am still testing it. I think it seems pretty accurate so far, and the app is great. My main gripe is that wearing it is a bit odd, and not something I would do for months on end, like I would other trackers. I haven’t used the Philips, but it looks to me like they copied Dreem.

  2. Thank you for the article. It is the best information about the reliability of sleep trackers that I have been able to find. I’m surprised that more manufacturers have not done studies comparing the results of sleep stage tracking via their devices with the results obtained via concurrent polysomnography. Perhaps the lack of such published results is because such studies have been done, with unflattering results. It would seem that the manufacturers would be touting great results if they had them.

  3. I’ve just completed a study (as participant, not researcher) using two sleep trackers, both by Withings: the mattress sleep pad and the watch. The watch is called Steel; I have no information on the name of the sleep pad.

    I have serious doubts about the accuracy of either device. Certainly the two devices show entirely different sleep stages for the same night, which gives me no confidence in either one. The sleep pad is somewhat better at showing when I’m in bed but awake, but — as you say — I think it considerably overestimates the time I’m lying still but awake. In fact, I have a habit of lying still for an hour or more, lying on my back, before I roll over to my side to try to sleep — and it doesn’t show that time at all reliably. The watch, for the most part, often shows no time in bed awake at all.

    I also dislike the pseudo-certainty with which both devices present their sleep stage data. Each stage is shown as a neat rectangular bar in a bar chart, giving the misleading impression that the diagnosis of sleep stages is precise and accurate — which I seriously doubted even before reading your article.

    The other concern I have with the sensors is that I have a waterbed (semi-waveless, so waves stop propagating after a few seconds). The waterbed has many virtues as far as my sleep goes — for one thing, I can adjust its temperature — but it was not possible to put the sleep pad under the mattress. Instead I put it on top of the mattress but under a quilt I use for a mattress pad. The sleep pad had a tendency to move around, too, so it was not always under my chest; quite often it was under my waist instead.

    One of the researchers told me that likely the waterbed made the data less accurate. Do you have any idea whether that is so? I’m especially interested in the accuracy of the heart rate data, as my heart rate (according to the sleep pad, anyway) goes surprisingly low — usually into the 50s, lowering gradually through the night.

    • Hi Mia
      Thanks for sharing your experience. I don’t really know if the waterbed will have a dramatic effect on the results, but my gut feeling is to say it probably does. Having said that, I also suspect the data would still continue to disappoint you a little even with a normal mattress – such is the nature of the tech currently. As for your heart rate, my nighttime resting heart rate averages 53-55. So I wouldn’t worry about it unless you also feel there is something wrong with your body in addition to the tracker data.

  4. Thank you for the interesting article. I have had sleep problems for decades. I usually only sleep for 2 to 3 hours per night even though I am in bed for 8. I have seen many specialists, and participated in many studies with no solution. One trick I use to get “rest”, is to lay perfectly still and ignore my body’s roll over requests. This puts me into a meditative out of body state that gives my body physical rest even when my mind is still active.
    My Family Dr recommended getting a smart watch for tracking sleep and activity. I will have to show him this article. I have noticed that the watch often tracks that I fall directly into rem sleep when I am actually laying awake and still in my meditative state and that the whole time I lay quietly in bed, it reports that I am sleeping either lightly or rem.
    Thank you again for the article.

    • Hi George
      Thanks for your comment – I’m happy to hear you liked the article. I’ve had similar issues when meditating in bed. It seems that lying very still for extended periods and perhaps lowering your heartrate consciously through meditation confuses sleep trackers even more than just watching TV in my experience. It’s a tricky one if you want to measure your sleep!

    • George, I had a similar problem! I suggest you watch Dr. Stasha Gominak’s conferences on youtube regarding the link between sleep disorders and Vitamin D deficiency. I raised my Vitamin D level from 8 ng/ml to 50 and things are much better.

  5. Interesting article thanks. I recently got a Fitbit Versa Lite, and it seems to track my sleep pretty accurately. However, my husband has slept with it 4 times now, and it shows him not going to sleep until 1:00, or 4:00 am, even though I know he’s asleep at 11:00. This has happened each time. Why would this happen when it seems pretty accurate for me?


    • Hi Kim
      I’m not sure to be honest. Perhaps it has learned your heartrate and movement patterns, so lending it to him for just a couple of nights is confusing the tracker. Perhaps try giving it to him for a couple of weeks and see if the accuracy stabilises.

  6. I have recently used the fitbit charge 3 and samsung active 2 and both listed my deep sleep as 0-1٪ I have a diagnosis of fibromyalgia and wake up 2 or more times in a normal night. Besides that I do everything by the book, sleep between 7 and 9 hours; fall asleep and wake and at a regular time, sleep in a quiet dark room, keep a healthy diet and don’t eat or drink much before bed… I always feel tired or fall asleep when I focus, read, watch a movie, or sit for more than 15 minutes. Do you have any advice besides getting a sleep study?

    • Hi Stu
      Thanks for sharing your experience. The only advice I can really offer is my opinion that home sleep trackers like yours can’t be relied on 100% for sleep stage tracking. I know it’s upsetting when you see something looks wrong with your sleep patterns – especially if you also feel that you’re not quite right in your daily life. I’d say the first step is to talk to your personal doctor/physician to see what they think about your diagnosis and apparent lack of deep sleep. They can advise you whether they think there’s a good reason to have a sleep study done.

  7. I had a Fitbit Alta HR for many years. I had thought it was pretty accurate on getting my sleep time and ok in stages. I wanted to have email and voicemail access on a watch, so I just got a Samsung Galaxy Active 2. The HR and sleep tracking are like night and day. The Fitbit stays more level whereas the Active 2 is very fluctuating on constant monitoring. I have AFIB, irregular heartbeat and extra heartbeat. I have just come to read that the Active 2 measures sleep by the heartbeat alone. The Alta HR measures a combination of heartbeat and movement. This may be why I seem to be getting a more accurate reading.

    The last three nights with the Active 2 have been all over the place. It cut off 2 hours in the morning when I was asleep. It starts too early (I only can assume as I am sitting up reading in bed and it thinks I’m asleep). Then it says I only had 12 or 11 minutes of deep sleep. Can that be? The Fitbit says I had an hour and 4 minutes of deep sleep (I’d rather believe that one).

    I have read on the Active 2 guide that if you have irregular heartbeat, you will not get a correct reading either on HR or sleep. I did check the heart rate with my blood pressure monitor which tells your heart rate and if you are in AFIB. That synched perfectly with the Fitbit, but not with the Active 2.

    There is a setting on the Active 2 to change it to Movement and you won’t get a deep sleep reading, but more of motionless, etc. I will try that to see if it is better. I kind of rely on my Fitbit for sleep information as you cannot combine both HR and Movement with the sleep tracking on the Active. At least I can detect changes, but I really don’t think I only got 12 minutes of deep sleep.

    Maybe I should stay with the Fitbit line. Factoring in both might be better than one or the other, or am I out of luck because I have all these heart issues?

    I was able to tell whether or not I was in AFIB by my pulse rate skyrocketing on the Fitbit. The Active has double the sensors which I can understand why the heart rate is so erratic as it may be more sensitive, but I can’t figure out the sleep tracking or how it could get more accurate.

    • Hi Lisa
      Thanks for your comment. Unfortunately, you’ve highlighted more than one issue that personal sleep trackers have. Firstly, they don’t all agree on sleep stages etc, because none of them have been found to be completely reliable, and some wildly innaccurate. That’s why I always say take sleep stages with a pinch of salt in general. Secondly, sleep trackers can be reaonably good when the conditions help them – i.e. you get a fairly solid night’s sleep without too many interruptions, you don’t lie in bed relaxing or awake and just motionless, and you don’t have other issues to skew the data (like a heartrate that confuses them!).
      So in your situation, I’m not sure what I would do – probably take all of the data from both trackers with a skeptical eye. I think it’s fine to use the trackers to motivate you to keep to a good sleep schedule etc, and perhaps look for patterns over time. But I wouldn’t rely on them, or make too many important decisions based on the data they provide. In terms of sticking with Fitbit or not, well, I like Fitbit, but also accept they aren’t perfect. I use them not just for sleep tracking though, but also for the smartwatch features and activity tracking, along with some other Apps that I enjoy having on my wrist. But you can get all that with other brands too!

  8. Excellent article, thank you. I have been monitoring my sleep lately with a Fitbit Alta HR, since I recently had a knee replacement. And like the first one 20 months ago, my sleep is seriously disturbed by the discomfort. I had a couple of full sleep studies as I have sleep apnea, and I think I am pretty self-aware of my sleep situation. So far I think the Alta HR is approximating my sleep reality pretty accurately and I am focused on getting more deep sleep and less light sleep. The feedback helps me to take steps to create best sleep conditions possible and its way better than Finding a night in a sterile sleep lab with guck in my hair and wires taped all over :-)

    • Hi Liz
      You’re welcome! It’s nice to hear you’re happy with your sleep tracker. I think it’s important to create the best conditions possible for sleep, no matter what a sleep tracker says – and especially if you have a diagnosed sleep disorder. I always make as much effort as possible to ensure my bedroom is just right for sleep – recently I think I’ve become even more convinced that the temperature is the most important factor for me – so I always pay particular attention to that, even preparing the bedroom well in advance to ensure it’s the best temp. when I go to sleep rather than getting into bed and then deciding if it’s too hot or cold and then waiting for my efforts to change the temp. to take effect.

  9. Hi.. so I have both insomnia and hypersomnia (it takes me alot of time to sleep. Once I sleep, I sleep a lot and during the day, I’m frequently drowsy and I frequently nap). Any recommendations for a sleep tracker (probably on the wrist) that would record my nodding off(s)?

    • Hi Hashem
      The problem is that sleep trackers usually don’t start recording sleep until a set time has passed – an hour for example. So if you nod of for 5-20 minutes, they will probably not record sleep. This is to stop them accidentally mistaking for quietly resting, reading, watching TV etc as sleep. You would need to check carefully the different devices to see what recording options they have. But all the ones I’ve tried so far don’t have a short nap recording function.

        • Hi Amrit

          It didn’t have the option to set it manually to record the nap though do it? And do you know roughly how long the naps were that it automatically picked up on?


      • For the past year or so, I have been wearing both a Fitbit AltaHR, and a Huawei Band 2 Pro fitness band, both on my left wrist, for activity and sleep tracking. I work from home, and sometimes take a late afternoon nap if sleepy. I use an extra kitchen timer I keep next to my bed, and usually set it for 20 minutes – so nap time is 20 min minus the few minutes it takes me to fall asleep.
        The Fitbit rarely or never has detected my 20 minute naps – either never, or a few times but I did not notice it in the data. However, the Huawei sometimes detects when I take a nap. I don’t know how often, but my guess is about 50% of the time.
        I don’t think either device can be manually started/stopped to record naps.

        However, I also have an older Fitbit One device. It was made to clip onto your waistband, but there are 3rd party wristband holders you can buy to wear the Fitbit One on your wrist. The Fitbit One only records sleep manually – you press and hold down a button to start a timer, and press and hold again to stop timer. It records total time and minutes of restlessness. So if you can find a used Fitbit One online, you could use this to manually time your naps.

  10. Thanks for this great article!

    Some years ago, I’ve been using the Sleep Cycle app on my iPhone (when you still had to place it on your bed) for a while and just recently re-downloaded it to use with my watch. What I’m most curious about, and what I can’t really find anything on: How does any accelerometer-based sleep tracker identify between SWS and REM? Sleep Cycle doesn’t provide information on time spent in REM sleep, but I’ve seen other apps that claim to do this. During both SWS and REM the body is as good as motion-less (completely relaxed during SWS, actually paralyzed during REM). You mention there has been some science to show that generally accelerometers are a good indicator to track sleep, but this keeps puzzling me. I’m wondering this because if, for example, a person spends a lot of time in REM but actually lacks SWS, this would give false positives as the wearable would pick it up as “deep sleep” due to a lack of movement? Obviously, any wearable can only give an indication of sleep quality past the total duration of spending in bed and maybe waking up during the night, but I’m really curious as to whether or not these two phases can actually be differentiated just by movement alone

    • Hi Anke
      Thanks for your comment. I think that’s a good question, and I personally don’t think any personal sleep tracker can be relied on to provide completely accurate breakdowns of sleep stages based on movement alone. I think including heart rate monitoring helps, as it provides another measurement beyond simply movement.
      But until respected sleep experts publish a definitive study of wearables or non-wearable sleep trackers in a lab, compared with a polysomnogram, and announce in a scientific journal that ‘we can now trust these devices’, it’s probably best to take the readings with a pinch of salt still.

      • I have to wonder if perhaps another data point that could be useful to incorporate with the accelerometer and heart rate data may potentially be a skin contact thermistor. How useful this might be would certainly require some research especially since the wrist could only give a rough approximation of core temperature and the diurnal variation in core temp is rather small at best. Still potentially with some clever algorithm and in concert with other data points it could perhaps be potentially useful at least given the practical limitations of externally wearable technology for constant wear.

        In an ideal world having health sensors in key areas thoughout the body would give the best results but people naturally are not likely to be comfortable wearing a massive wiring loom and sensors all over externally so short of moving to implantable sensors it’s probably the closest we could get for now doing what can be done with a simple relatively unintrusive external device.

        • Hi Matt
          Thanks for your comment. It’s an interesting proposition – I wonder if any of the tech companies are working on something like this for the future. What’s clear is that better measuring tools are needed, whether it’s a worn or contactless sleep tracker. I hope the puzzle is cracked before too long, but without resorting to too many wires, as I agree – that wouldn’t exactly be appealing to many people.

  11. I have recently bought a fitness tracker wristband made in China using H-band App and bluetooth communication with my smartphone.
    The tracker measures the usual movements also Heart Beat Rate and Blood Pressure with LED light technic. I do not know if the sleep tracking funtion use those functions. I can see some accuracy in the sleep result presented but also some discrepances especially when staying in bed or even going up and sit watching television and eating breakfast. The sleep tracking starts automatical after 10 pm up to 8 am. I have understand that to end the sleeping period I have to do more movement than just going up from the bed to the toilet and then sit rather still or go back to the bed but not to go on sleeping.
    I know that I snore a lot but that is of course not shown in the sleep result quality. I normally get lot of deep sleep time especially in the last hours of my sleeping period. With the smartphone included in the sleep tracking system a registering of the snoring sound sleeping alone could be of interest I think.

    • Hi Gunnar
      Thanks for your comment. I agree that moving a bit more can help to tell the tracker that you’re awake now. If you do go back to bed and relax, even just moving your arm from time to time might help. But it’s a shame they often mistake relaxing for sleep. As for snoring, there are a couple of that do that. You can also get phone Apps that will listen out for snoring.

  12. I’m using the BeautyRest SleepTracker (yes, it’s the mattress people). It costs about $70 and comes with two under-the-mattress sensors, although I use only one. Every morning, about 30 minutes after I get up, there’s a report in my email inbox. The graphics are stunning and I view the reports on my iMac, full screen, which is much more satisfying than on a phone. I bought it to record my trips to the bathroom and it nails them very accurately. So far as I can tell, its heart rate and breathing rate numbers have no connection with reality, but their graph lines do show gaps at the right times.

    • Hi Charles
      Thanks for your comment. I’m actually in the middle of writing a long article detailing a test I did where I used the Beautyrest tracker, Emfit and Fitbit Versa for a few days at the same time. I was quite impressed with the Beautyrest. Like you say, it’s good at spotting wakings, and the graphics and fantastic. I’m not so sure about some of the finer points like sleep stages, but it observable seems to do the basics pretty well.

  13. Thanks for researches and efforts, the article was illustrative.
    I am a 58y old female with serious insomnia issues, sometimes not sleep at all during the night. 2 weeks ago I bought some cheep no-name bracelet, for running purposes actually, but found myself very surprised on how accurate it traces my sleeping phases. Of course I can’t control the difference between deep and light sleep to be compared with the device reports, but awaken phases in between are spotted perfectly.
    Moreover, I am experiencing better sleeping with the bracelet for a funny fact – that I am taking my sleeping issues more seriously because of data tracking and put myself to bed when needed (at the evening instead of previously at the mornings or not at all). Good start I think :), so I am greeting very much a fast development on this kind of toys.

    • Hi Mg
      Thanks for your comment. Although I always say to take the sleep stage data with a pinch of salt, it’s good that you feel it’s getting the timings you can check yourself right.
      And if it’s encouraging you to take steps to improve your sleep, that’s a good result!

  14. I have been diagnosed with narcolepsy and take medication twice daily to stay awake. I just started using an app on my iphone6 called Sleep Cycle to track my “deep” sleep which is a deficit in narcolepsy. Each night the sleep data is recorded as a graph and it very interesting to see the variety of waking & “deep sleep” cycles. The research shows that movement is the indicator for “deep sleep” in all the sleep trackers. That being said, I am using Sleep Cycle to track my sleep patterns and keep me honest as to my actual bedtime schedule!
    Thanks for the info on your blog,

    • Hi Keynsham
      Thanks for your comment. I know Sleep Cycle is a popular App. Just to correct something you said though – some sleep trackers also use heart rate to help determine which sleep stage you are in. But really, none of them can be completely relied on to accurately track sleep stages still – though they are getting better I think.

  15. I use the Fitbit Charge 2 and I find it very “hit and miss” regarding sleep tracking. I am recording my findings in the blog – some nights it seems spot-on, and on others COMPLETELY WRONG. I don’t believe that home technology is yet anywhere near the accuracy of an EEG, so sleep tracking on even the most expensive devices currently available is at best only a rough guide. I believe that the means to accurately measure your sleep at home is at least a decade or so away.

    • Hi Gary
      Thanks for your comment. You’re right in that home devices still need to be taken with a pinch of salt, and can’t compare to an EEG. Having said that, I’ve found both the Ionic and Alta HR to be more accurate than the Charge 2.
      Good luck with your blog!

  16. For several months I have been using the Fitbit Charge 2 which says I am not getting enough deep or REM sleep. I started using the ResMed S+ to compare results. Huge difference! S+ said I am getting 2 hours deep sleep and Fitbit says 38 minutes of deep sleep. Do you know why the difference and which would be more accurate?

    • Hi Jill
      Thanks for your comment and interesting question. It’s not as straightforward as saying one is the right amount and the other not, unfortunately. One major factor is your total sleep time. But unless you’re sleeping for a really long time, that 2 hours sounds like a lot to me. Then again, the 38 mins could be an underestimate if you’re getting a good night’s sleep. But really, considering the inaccuracies that crop up with sleep trackers, you might find the truth is somewhere in the middle! What does your fitbit tell you when you look at the benchmarking with other people your age?

  17. Thank you. This is a much needed article. Sleep Apps for wearables are in danger of over promising. In my experience they don’t clearly set out how they work and their limitations.

    I use an Apple Watch App called Pillow, have you reviewed this?

    • Hi Dan
      Thanks for your comment, and I’m glad you liked the article. Yes, it’s a shame really that they aren’t so reliable! I have plans in the pipeline to do a huge test of lots of different ones all at the same time. I’d love to take the test into a sleep lab to compare them with their equipment, though it might not be possible. If I do manage to get round to this kind of test, I’ll be sure to write about it!
      And no, I haven’t used that App – can you tell me a bit about it?

      • Hi, I use the Apple Watch + Pillow as well. Ten years ago, though, I had the original Zeo with the headband and everything. After it died I went a long time with no tracking. Did you ever have a chance to compare it against the modern set of trackers?

        • Hi Nate
          Unfortunately not, no. I wanted to and then it was discontinued just as I was getting around to it!

  18. Hi, thanks very much for your comprehensive and sensible explanation of how sleep trackers work and comparing different devides. I’m 65, female, and over the past couple of years my sleep has been getting less restful. So a few months ago I bought a Fitbit One. Though the accuracy is questionable, comparing its results over many weeks gives me a general sense of how I sleep each night and is actually quite reassuring. It does confuse sleep with awake-still, but the latter state can be restorative too. I’m looking for a device now that checks more factors than just activity and will give a more defined readout. Your articles have been very helpful in choosing which one to purchase. Thank you.

    • Hi Sharon
      Thanks for your comment. I’m glad you found the article helpful – thanks for saying so! The Fitbit One is definitely at the lowed end of the market in terms of what you can get from it, and you’re right in that the sleep readings can be questionable, but over time give a general idea. Hopefully you’ll get some more interesting data with your next choice of sleep tracker.

  19. I am just wondering if it is also meaningful to have a sleep tracker for baby? Is it meaningful to consider to improve the baby’s sleeping quality – as it sounds babies are always sleeping no matter what environment they are in. But if there is a sleep tracker for them, maybe their emotion can be understood better for “day time” as they cannot “speak” out what they need. If there is some ways to improve their sleeping quality, will it be helped their brain development?
    I believe it is not necessary for the tracker to wrapped around the wrist but anywhere in the body, just for the wrist, the movement is the “most obvious”.

    • Hi Linda
      Thanks for your comment. To be honest, I’ve never heard of anyone using a sleep tracker for a baby. I think the way they are calibrated, you’re likely to get lots of warnings about sleeping badly because of waking up too often and then sleeping for too many hours during the day, so I can’t see that it would be helpful.
      Having said that, there are loads of Apps for babies which take into account things like sleep and sleep patterns. If you have a look online, you’ll find plenty of reviews of them that you could read through and see if any do what you’d like it to.

  20. Hello Ethan, I have RLS (Restless Leg Syndrome) and take drugs to help the symptoms but I never feel like a have a restful sleep, I wake up exhausted and tense. I don’t care about daytime activity monitoring, just my night time … dare I say “sleep” and what is happening during the night. Can you recommend a type of monitor that would be useful for this type of issue. Thinking to maybe use it to help adjust my medications with my doctor. Oh, also don’t want to spend tons of money either ;-).

    • Hi Alden
      Thanks for your comment. Even though you’re not interested in activity tracking, you might find a wearable device helpful because they work mainly based on movement. So if you move around a lot in the night, they might pick up on that and record it as restless sleep or being awake. But then again, most of the bed based ones will also tell you if you moved around a lot in the night! So if money is also a factor, I’d go with one of the cheaper ones first and see if it gives you the results you’re interested in. What you’re asking for isn’t anything particularly unusual for sleep trackers, so you’ll find most of them will try to record how much you’re restless.

  21. I’m looking for a sleep monitor that will record my heart rate continuously. I have sleep apnea (I use a CPAP) and I want to see my HR on a graph because I know apneas cause a slower HR and then a higher HR afterward. My DreamMapper app doesn’t give me a graph just the number of apneas per night. Sleep stages would be nice, too

    • Hi Alice
      Thanks for your comment. Many wearable sleep trackers give you your heart rate readings these days. But are you looking for one that will track apneas and correlate it with your heart rate? If so, I’m not aware of one that does that.

    • Suggest you try an inexpensive recording finger pulse oximeter. When you download the data in the morning, you’ll get O2 desat and heart rate tracings thru the night. The CMS 50D+ goes for less than $40.

  22. Hello, I took a sleep test and was diagnosed with moderate sleep apnea. After trying different solutions I settled on a customized mouthpiece built by my dentist to increase air throughput. I then went back to take the sleep test with my mouthpiece and the result was I don’t have sleep apnea when wearing the mouthpiece. Although it is night and day compared when I wear the mouthpiece vs not wearing it, I also notice some days are even better than others when wearing the mouthpiece. Which device would you recommend that provides more accuracy for REM and deep sleep per night?

    • Hi Dion
      Thanks for your comment. It’s great that you had such good results with the mouthpiece! To be honest, I don’t think any of them are 100% reliable when it comes to breaking down the sleep stages. However, I’d probably recommend one of the stand alone devices over a wearable one. Have a look at the different ones and see which you like the sound of based on the other features it offers too.

      • Headband Dreem 2 claims accuracy of sleep stages: 75%

        Garmin recently published an overall accuracy of: 69.7%

      • Hello Ethan,
        I’ve got a top range new Garmin. My view is that it’s more accurate than my previous Huawei watch but should be for the extra price. It’s the sleep stages that worry me. Rem/Deep & light sleep. Not sure it always knows the difference between REM & Deep sleep. But I have noticed one very interesting thing. On nights I’m in with no alcohol it shows a much higher overall score for sleep quality. However the 2 nights after 2 glasses of red wine, the score drops significantly. And we know what they say about sleep quality after alcohol. So it seems to know the difference. Interesting. Peter

        • Hi Peter

          Thanks for sharing your experience. I always say to take sleep stages with a pinch of salt, no matter which device you use. I think the sleep score / total sleep time is interesting as it often seems to show an effect based on lifestlye choices like alcohol. I’ve noticed exactly the same thing in the past with my Fitbit when I used to drink alcohol.


  23. I am 72, in good shape, still working, doing sports and other activities. At about 10pm I am tired and wish to sleep. As soon as in bed, my tiredness gone and I waste time in bed untill 2am and sometimes even longer. When asleep. I sleep rather well until about 8am. Could you recommend devise which would improve my sleeping habits?

    • Hi Dov
      Thanks for your comment. Many devices will encourage you to stick to sleep goals that you set yourself. So you can say what time you’d like to go to sleep and wake up, and they will give some kind of positive or negative feedback if you get within a target range of that. Fitbits have that option for example, but others do too.
      To be honest though, the best way to improve your sleep habits is by planning them yourself. It may be that in your case, you’re feeling tired but not ready to sleep. I’d have a look at my article about fixing your sleep schedule where I explain more about that.

  24. My husband was given a Fitbit Flex & we both tried it for sleep monitoring. It didn’t work well (and was very inaccurate at measuring steps & activity, too, but that’s a separate problem).. I especially remember that the Flex said I woke up 46 times in one night… what actually happened that night is that I slept little, and only in 2 or 3 spells. I wish something was a decent monitor, although what I really want is just to sleep better over all. Nothing works, argh.

    • Hi Julii
      Thanks for your comment. I had a Fitbit Flex some time ago, and remember being less than impressed by the general accuracy. Having said that, I’ve found other Fitbits more accurate, namely the Charge 2 and Surge.
      But yes, it’s unfortunately the case that sleep trackers get confused between awake and still or asleep. So if you’re awake and still a lot, trying to sleep, but then inevitably toss and turn frequently, it might think you were asleep and keep waking up. That’s why I think sometimes when you have a particularly bad night, it’s good to correct the information manually the next day on the App. Though of course, in an ideal world you’d never need to do that because it would be totally accurate! Have you tried any of the other bed-based trackers, like the Withings Aura, Beddit or Sleepace, or perhaps even the S+ by Resmed? It might be worth trying one of those to see if it’s more accurate for you.
      As you say, the main thing though is to sleep better overall. And for that, there’s plenty of advice around this website. If you haven’t already taken a look, I highly recommend having a look at the sleep hygiene section, where I’ve tried to compile as many good ideas for better sleep as I could.

  25. In a very short test period, I have noticed that my wrist monitor only seems to tell me I have been in Deep Sleep at times when my wife is not in the bed alongside me.

    Does having a partner in bed with you affect the results if they are restless during the night??

    • Hi Alan
      Thanks for your comment. It depends which sleep monitor you have, but it’s definitely possible. Which one are you using? I think more so with those that have measuring strips on the bed which your partner can touch with their body. Wearable trackers on the wrist I think are harder for a partner to disrupt. But just thinking off the top of my head, I wonder if a partner is very restless, perhaps it could make you more restless if you’re a light sleeper? I have no evidence for that idea though – I’m literally thinking out loud here.

  26. I am searching for a device to monitor my sleep. Like susan I have narcolepsy but I’m not sure that’s relevant. I feel like there’s a lot of moment where I am awake in the middle of the night and I would like to monitor it in order to give like a sleep diary to my slepcialist. I think the Jawbone UP3 could do that. I could use only at night (seems that the bracelet is not lasting long…). I found on other device the ability to add hashtag to the day to see what factors could improve or damage sleep quality. I’d like to have that but I’m not sure the UP3 does that. Anyhow, it happens also often that I fell asleep while I didn’t plan to do so and start my night too early, often I wake up to put my night cloths as others people would do to pee but I have no idea how long I’ve been sleeping, what does it do to my sleep cycles, etc. I could do a basic diary with a pencil and everything but I know I woul forget at some point to do it.

    • Hi Sabine
      Thanks for your comment. I think the main thing for you then would be one which records sleep automatically, rather than having to tell it yourself that you’re going to bed now. The UP3 will do that. And then one which is particularly good at recording nighttime wakings. Again the UP3 will do that, but then so will many others. The good thing about the UP3 is that it’s very inexpensive compared to many others. So if you want to try one, but don’t want to spend too much, it’s a good choice. However, if you want to get a really detailed view and aren’t interested in activity monitoring during the day, you could perhaps try one of the bed based ones such as the withings aura or beddit.

  27. My intention is to measure ‘how much’ I sleep rather than ‘the quality’ of my sleep. Meaning assessing depression not insomnia. I currently use the leaf and love it except it only tracks sleep for a defined period, not 24 hrs: 9PM – appears to be 10 AM. To credit the Leaf you have the ability to add naps but I would prefer to not do so everyday.
    So I’m looking at google apps that would allow me to turn it on and off, on and off with nap, on and off with nap, on sleep….. I’m sure there’s something but I feel the market is more geared to insomnia. I’ve a sleep test but it wont definitively track time.

    • Hi Amy
      Thanks for your comment. Many, if not most, sleep trackers allow you to manually input the time you went to sleep and woke up, if that’s what you mean? But if you want one which is constantly on and automatically monitors your sleep 24 hours a day, you can get that also.

  28. I have been using the Fitbit Flex to monitor sleep . I have narcolepsy and and am on Adderal for daytime sleepiness . Have had a sleep study to confirm . I usually wake at 9 00 and go to bed at 11 30 . My age 68 yrs . I sleep about 5 to 6 hrs , according to Fitbit .. I feel exhausted after waking up until 12 00 or so and then have about 7 hrs of fairly productive time . I guess Fitbit must be right. I wish I did not have to spend so much time in bed to get so few hrs of sleep.

    • Hi Suzanne
      Thanks for your comment. It’s interesting that the Fitbit is reflecting what you think is the case with your sleep – that’s a good thing! Yes, it can be frustrating to be in bed and not sleeping. Have you spoken to a sleep specialist about your sleep schedule? Perhaps they can suggest a routine for you that isn’t so frustrating.