The most accurate sleep trackers in 2022

Sleep trackers are devices that measure your sleep. They are growing in popularity because monitoring the quantity and quality of your sleep helps improve physical and mental health (to understand better what sleep trackers can do for you, see this post). The problem is that there are dozens of sleep trackers available today, varying in price, format, and quality. In this post, I review the six most popular sleep trackers on the market. I describe their features and report the scientific evidence in favor of their accuracy so that you can make an informed decision.

What kind of information can you get from a sleep tracker?

Sleep trackers provide two main kinds of information: Total sleep duration and sleep quality, measured by the time spent in the different sleep stages. There are five sleep stages:

  • Two stages of light sleep. They occur right after you fall asleep and start each new sleep cycle (Stages 1 and 2).
  • Two stages of deep sleep (Stages 3 and 4).
  • Rapid eye-movement (REM) sleep (Stage 5).
Sleep cycle. Stages 1 and 2 are identified as light sleep; Stages 3 and 4 as deep sleep; and Stage 5 as REM sleep.

What makes a good sleep tracker?

In my opinion, three main criteria matter when choosing a sleep tracker:

  1. It should be accurate. Accuracy is the most important feature because what’s the point of investing in a sleep tracker if you can’t trust its data? You will find several reviews of sleep trackers on the web (e.g., see here, here, and here) but interestingly none of them mentions their accuracy.
  2. It should be comfortable enough and not disturb your sleep. Commercial sleep trackers can take different formats: smartphone apps, boxes to place on your nightstand, watches, rings, and under-mattress pads. What is comfortable varies from person to person. Personally, I don’t like wearing a watch or having my phone in my bedroom. But it’s up to you to judge which type of sleep tracker is right for you.
  3. It should be affordable. The prices of sleep trackers vary quite a bit, from a few euros a month for a smartphone app to several hundreds of euros for the most sophisticated devices.

I want to apologize about the next paragraphs because I’m about to get nerdy and provide a bunch of scientific information about sleep trackers. If reading the next titles already makes you yawn, then skip to the preview below. I won’t be offended, I promise. But, if like me, you like to judge for yourself the quality of the devices you buy and get a glimpse into the science of sleep tracking, then allow me the pleasure of taking you on a geeky ride.

How is the performance of a sleep tracker measured?

Researchers assess the accuracy of sleep trackers with three main values:

  • Sensitivity: the ability of the sleep tracker to correctly detect sleeping episodes (true positive rate). Sensitivity = True sleep duration / Measured sleep duration
  • Specificity: the ability of the sleep tracker to correctly detect wakefulness episodes (true negative rate). Specificity = True awake duration/ Measured awake duration
  • Accuracy, which combines sensitivity and specificity. In other words, it’s the ability to identify both sleeping and wakefulness episodes. Accuracy = Number of correct assessments/Number of all assessments

Scientific studies also report the performance of a sleep tracker in identifying the stages of a sleep cycle by calculating for each stage its sensitivity, specificity, and accuracy. To better understand how to interpret these values see this article.

The method that I followed in my investigation

As a scientist, I find it essential to be transparent regarding the method that I used to find the best device(s). Here is how I proceeded:

  1. I searched the web for the most cited sleep trackers and came up with six devices.
  2. For each sleep tracker, I gathered in the table below central features such as the device type, its price, and the measurement it collects.
  3. Then I looked for scientific investigation into the performance of the device. I focused on peer reviewed articles and abstracts, i.e., research articles that have been reviewed by independent scientists and published in journals recognized by the scientific community. I gave special consideration to meta-analyses because they include a larger number of peer reviewed studies and provide more reliable results. Finally, I privileged research that compared the performance of the sleep tracker to polysomnography (PSG). PSG is the scientific gold standard to assess sleeping patterns. In simple terms, PSG connects with many electrodes the sleeper to an electricity measuring machine. It’s a cumbersome, expensive, and complex machine. You cannot use at home, but it’s the most accurate sleep tracker. Therefore, the correct way to estimate the performance of a wearable sleep tracker is to assess its accuracy based on PSG results.

Disclaimer

I want to make a couple of points clear before moving on to the results.

This blog post is not a scientific review of sleep trackers. I’m a neuroscientist, but I’m no sleep expert. Moreover, I looked for the papers I could find on the websites of the sleep tracker companies, and, if I didn’t find any scientific publication there, I looked more generally on the web and in scientific search engines (e.g., PubMed). I assumed that if there were published research supporting the performance of a sleep tracker, the company would mention it on its website, but I may be wrong. And I didn’t contact the companies to check that with them.

This review reflects my opinion based on my research and experience with these devices. I tried some of them myself: I’ve bought the Oura ring and tried the trial version of the Sleepscore app. I’m not sponsored by any of these companies, but I have affiliate interests with products bought on Amazon.

Sleep trackers overview

The table below offers an overview of the six sleep trackers I investigated. I’ve ranked them in order of performance (1 being the best).

DevicePriceMeasurement(s)Scientific evidence of accuracy
1. Oura ring€314-419 for the ring+ monthly membership of €5.99Heart rate
Heart rate variability (HRV)
Skin temperature
Movement
The 2022 ring should track blood oxygen levels (SpO2 sensing)
Good
2. Sleepscore smartphone app€8.99 for the premium version of the app
€149.99 for SleepScore Max (box to use in place of the smartphone)
Non-contact sonar sensor technology that tracks the sleeper’s movements and respiration in bed.Good
3. Fitbit smartwatches€149.95-299.95 + monthly membership of €9.99 Heart rate
Skin temperature
Movement
Blood oxygen levels (SpO2 sensing)
Good
4. Withings Sleep
(under the mattress pads)
€129.95Body movements
Breathing patterns
Heart rate
The pads have been used in peer-reviewed scientific studies on sleep but I couldn’t find any validation study reporting their accuracy
5. Sleepon Go2sleep Tracker (under the mattress pads) $129Heart rate
Heart rate variability (HRV)
SpO2 (blood oxygen level)
Perfusion index
I couldn’t find any scientific study reporting accuracy
6. Tempur-Pedic Sleeptracker
(under the mattress pads)
$349Micromotions used to infer:
– Body movements
– Heart and respiration rate detection
I couldn’t find any scientific study reporting accuracy
The prices mentioned in this table are those published on the companies websites at the date when I’m writing this post. They may be subject to change.

1. Oura ring

The Oura ring is an elegant ring that tracks several physiological factors (see table above). 

Scores & features

Every day you receive three scores:

  • A sleep score: How did you sleep last night? This score derives from the analysis of light, deep, and REM sleep, as well as nightly heart rate, bedtime schedule, and more indicators.
  • An activity score:  How are you balancing your activity, inactivity, and rest? This score relies on daily movements, training, and recovery time.
  • A readiness score: How much can you and your body take on? This score depends on the sleep and activity scores as well as physiological stress signals like body temperature and heart rate variability (HRV).

In addition, the app offers several features such as the use of body temperature information to predict female period and warn when you may be sick, activity detection (sports), calorie burn, guided meditations, etc. 

Accuracy

The Oura company works with renowned sleep scientists, such as Matthew Walker. The ring has been used in several peer-reviewed studies, one of which has investigated its validity using PSG. The results of this study are encouraging:

  • The Oura ring does an excellent job at categorizing wake and sleep. Wake/sleep accuracy is excellent (96.38%), sensitivity good (80.74%), and specificity excellent (98.15%). 
  • Results concerning sleep stage detection are more mixed. The ring shows a good overall accuracy (80.2% to 90.87%), a sensitivity that is good for light sleep (81.7%) but poor for deep and REM sleep (74.44% & 78.08%, respectively), and a specificity that is poor for light sleep (78.67%) but excellent for deep and REM sleep (94.63% & 94.63%, respectively). 

In simple words, the ring can accurately report how long you slept and provides insight into the quality of your sleep. However, it also tends to overestimate the duration of deep and REM sleep and underestimate the duration of light sleep.

2. Sleepscore smartphone app

Sleepscore is one of the most often downloaded smartphone apps to monitor sleep. The idea is that you put your smartphone on your bedstand and a non-contact sonar sensor technology tracks the sleeper’s movements and respiration in bed. An alternative to using one’s cell phone consists in buying the SleepScore Max, i.e., a box that uses similar technology.

Scores & features

The app provides daily sleep scores with information such as:

  • Sleep duration
  • Time to fall asleep
  • Sleep stages
  • Wake time

The app also offers several other features:

  • Tips and information about sleep
  • Snore detection
  • A sleep library
  • An evaluation of the light and noise levels of your bedroom

Accuracy

The application has been used in several peer-reviewed studies (see here) and its performance has been assessed in several validation studies comparing it to PSG. The performance reported by these articles is not bad. For example, in one of the most recent papers, sleep accuracy was 84%, sensitivity was 65%, and specificity was 88%. This suggests that the app is quite accurate at estimating total sleep duration although it tends to underestimate it.

Concerning the sleep stages, the same paper reports a good accuracy (89% for REM and 83% for deep sleep), a low sensitivity (57% for REM and 62% for deep sleep), and a good specificity (93% for REM and 88% for deep sleep). These results indicate a good performance of the app in detecting REM and deep sleep stages although, here again, it underestimates their duration.

I must admit that I am surprised by these good results. I would never have thought that a tracker so far from the sleeper could be accurate. But the data suggest that it is. One limitation to keep in mind, however, is that the validation studies were done in controlled laboratory environments. I don’t know how the system performs in real-world situations when you’re sharing a bed with someone else.

3. Fitbit smartwatches

Fitbit watches are classical smartwatches with a sleep-tracking function. Fitbit offers several smartwatches – Versa and Sense – that differ in theirs features and prices, but as far as I can judge, the sleep-tracking functions of the two watches are the same.

Scores & features

The phone application associated with the watch gives you a general sleep score and the duration of the different sleep stages.

The watch also possesses several features that can be useful for improving your sleep and general fitness, such as:

  • silent alarm waking you up with a vibration
  • smart wake function that wakes you up during light sleep
  • Sleep insights and tips
  • Several smartwatch features, including a readiness score, health metrics (e.g., steps), mood logs, stress management tools (the app works with a Calm subscription), high and low heart rate notification, workout intensity map, menstrual cycle, etc.

Accuracy

The Fitbit watches have been extensively used in peer-reviewed studies on sleep and health. You can even find a meta-analysis based on 22 studies investigating the accuracy of wristband Fitbit models in assessing sleep. This study reports the following results:

  • Fitbit smartwatches have a good accuracy in detecting sleep duration although they tend to overestimate it. In comparison to PSG, the wake-sleep accuracy is good (range from 0.81 to 0.93%), sensitivity is excellent (range from 0.87 to 0.99%), but specificity is poor (range from 0.10 to 0.52%).
  • Fitbit smartwatches are not accurate in detecting sleep stages. Relative to PSG, accuracy varied between 0.69 and 0.81 in monitoring light sleep, between 0.36 and 0.89 for deep sleep, and between 0.62 and 0.89 for REM sleep.

Thus, Fitbit watches seem to be useful for estimating sleep duration and offer interesting features. However, if you buy one, you should consider with caution the estimation of sleep stage durations.

4. Withing sleep pads

Withing sleep pads are devices that you lay under your mattress.

Scores & features

The pads possess sensors that track breathing patterns, heart rate, and body movements. Data are sent after each night to an app on your phone. The app then provides you with several sleep scores:

  • Sleep duration
  • Sleep recovery
  • Sleep interruptions
  • Regularity
  • Time to fall asleep
  • Sleep stages tracking
  • Heart rate
  • Snoring episodes
  • Sleep apnea detection and severity

Accuracy

The Withing sleep pads have been developed with sleep physicians from the hospital Beclere in Paris (France). One can find several publications on the company website from well-known research groups who used the device for research on sleep, such as this one. But I couldn’t find any validation study that compared the pads with SPG. So, either I’ve missed the study, or it hasn’t been published in a peer-reviewed journal. 

5. Sleepon Go2sleep tracker

The Sleepon Go2sleep tracker is a ring with a small oval device facing your palm that is supposed to assess a whole range of physiological functions (see the overview table above). 

Scores & features

The app associated with the ring provides several daily sleep scores:

  • An overall sleep score
  • Sleep duration
  • Number of tosses and turns
  • Sleep stages
  • Sleep debt
  • Heart rate
  • Spo2

The ring also offers several functions, such as: 

  • Vibrotactile Feedback, which alerts you when your heart rate and blood oxygen level is abnormal during sleep
  • Body status
  • Bio alarm clock, which wakes you up in your lightest sleep phase
  • Possibility to share your data with family members

Accuracy

I couldn’t find any information regarding the performance of the device. I just found the review of a user who reported that data (e.g., sleep stages) was missing from the report some mornings. But, of course, this kind of evaluation should be taken with caution as it is just a personal experience. 

6. Tempur-Pedic

Tempur-pedic is composed of two sensors that you place under your mattress. They infer your movements, heart, and respiration rate from what the company calls micromotions. 

Scores & features

You receive on the app several scores:

  • A daily sleep score
  • A sleep efficiency score (time spent asleep vs. time in bed)
  • Sleep stages
  • Intense snoring detection

The app also offers several other features, such as: 

  • Personalized sleep coaching
  • Bedroom environment assessment: temperature, humidity, air purity, and CO2 levels near the bed
  • Couple’s measurements: One of the reasons why this sleep tracker is praised is that it would work well for couples. You have two sensors that you put on both sides of the bed, which should enable to separate information coming for each person (assuming they don’t spoon too much :-D)

Accuracy

I couldn’t find any information concerning the validity of these sensors.

In Sum

In this post, I reviewed six of the most popular sleep trackers currently on the market. Some of these devices seem to provide a good estimate of sleep duration and wakefulness. My preference goes to the Oura ring due to its excellent performance in assessing sleep duration. But the Sleepscore app seems also a good choice, especially if you don’t want to spend much money. Finally, Fitbit watches seem to provide useful data and have interesting features; however, one should keep in mind that they tend to overestimate sleep duration. 

Regarding the identification of the different stages of sleep, I am more reserved. Here again, the Oura ring seems to provide the best performance, but it is not totally satisfactory either. However, this technology is evolving so quickly that I’m confident that the next generations of sleep trackers will fill this gap. 

If you also use a sleep tracker or have more information about them, please share your experience in the comments. I’d love to know what you think.

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2 Comments

  1. Tor 16. February 2022 at 4:16

    This is an excellent analysis. Thank you for linking the papers. As a biosensor scientist, I agree with your skeptism of the sleepsmart app and the controlled conditions it was tested in. I am impressed by the accuracy of the oura rings, although wish they would have done a test using unseen data (the 5 fold cross validation will be a higher accuracy than if when the sensor is deployed for real life). Still it seems to be much more accurate than the other products.

    Reply
    1. Gayannée Kedia 21. February 2022 at 10:17

      Thanks for your comment, Tor!
      I’ve bought the Oura ring and I’m very happy about the sleep data. As far as I can judge, it seems pretty accurate. It detects well the moment when I wake up in the night, which wasn’t the case of Sleepscore.
      It also provides health predictions but there I’m a bit more reserved. It sometimes tells me that I’m in a great shape when I actually feel sick and vice-versa. Oura should release a new ring with SpO2 measurements in 2022. Maybe will this new version work better.
      Best regards,
      Gaya

      Reply

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