How Sleep Trackers Work
Tracking sleep at home is hard. In fact, its like trying to track an earthquake, said Thomas Penzel, PhD, research director of the Interdisciplinary Center of Sleep Medicine at Charité University in Berlin. Just as you cant sit inside the earth and watch tectonic plates shift, you cant directly peer into your own brain as youre sleeping. So you need proxies. In a sleep lab, scientists use medical-grade equipment and sensors to record brain activity, eye movements, body movements, heart rate, oxygen intake, and more. This process, called polysomnography, is the most reliable method of sleep tracking.
Unfortunately, the sleep trackers designed and currently available for home use cant read brain waves and eye movements, which most reliably track stages of sleep, so instead they guesstimate based on less accurate signs. The current technologies include the following:
Movement tracking: Accelerometersmore commonly used to measure sleep in fitness trackers and other wearables than in phone appsinterpret stillness as sleep and movement as wakefulness. But an accelerometer is not very accurate when you use one alone because it may perceive you as being asleep when youre merely lying still staring at the ceiling. And if you toss and turn a lot in your sleep, the accelerometer will register that youre awake. Thats why sleep tracking typically pairs movement tracking with other technologies, such as optical heart-rate monitoring.
Why You Should Trust Us
As a senior staff writer at Wirecutter, Joanne Chen has covered a range of sleep topics shes the author of our Five Days to Better Sleep challenge, our guide to sunrise alarm clocks, and our advice on how to choose the right mattress. For this guide, Joanne interviewed product specialists and brand executives in the sleep-tracking field and sleep doctors who have done their own sleep-tracking experiments either formally or informally, as well as a computer scientist who specializes in behavior tracking. Last, but perhaps not least, Joanne is personally familiar with professional-grade sleep tracking. She spent a restless night in a sleep clinic with her then-toddler son when she suspected he had sleep apnea. A few years before that, Joanne had shooed her husband off to the same clinic to have his snoring checked out.
Justin Redman is an associate staff writer on the sleep beat and has contributed to Wirecutters coverage of mattresses and other sleep products. As a below-average-to-poor sleeper for most of his life, hes always looked for tools to help him sleep better, from blackout curtains to nasal strips.
How Did We Find The Best Sleep Tracker
Weve gone above and beyond in our quest for the best sleep tracker to find options that will fit most needs and preferences. Whether you prefer a wearable sleep tracker that can monitor your activity throughout the day or non-wearable ones that are fitted inside or under the bedding, weve found the perfect solution for all your sleep-related problems.
Weve evaluated each sleep trackers price, features, customer reviews, and brand reputation to curate a list of the best sleep trackers in 2021. Its important to us that the sleep trackers we recommend are easy to navigate and effective and pair well with their companion apps to give the best user experience for an unmatched price.
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When To Contact A Doctor
A person might consider contacting a doctor if they get insufficient or low quality sleep. Sleep disturbances could indicate an underlying health condition or exacerbate other symptoms a person may have.
If a person uses a sleep tracker, they may find it helpful to bring the data to their doctor appointment, as this may help the doctor decide what tests to run or which treatments to recommend.
All of the data from sleep trackers should be available on the relevant app on the persons phone.
Here, we answer some of the most frequently asked questions about sleep trackers.
Signal Analysis And Algorithm
Besides the physical challenges of shining light through blood vessels and accurately capturing the reflection, its up to complex algorithms in the device to convert the signal into a more or less accurate heart rate reading.
One of the big issues at play is noise. For example, if the sensor doesnt have sufficiently tight contact with the skin, ambient light can interfere with the reflecting light from the LEDs, thus reducing the overall signal quality.
On the other end of the spectrum, a sensor that fits too tightly might restrict blood flow and thus also reduce signal quality. Either way, the resulting heart rate reading might be inaccurate.
Consequently, if the HR reading is inaccurate, the resulting sleep monitoring will be as well. In my experience, most standard straps that look like regular watch straps dont provide a good enough fit for the sensor to remain in constant contact with the skin.
Thats why I use the Sport Loop *with my Apple Watch and the ProKnit strap with my WHOOP*. Regardless of what brand or type of device you choose, make sure it comes with a good strap that can be easily adjusted for a perfect fit. Trust me, that makes all the difference!
The second influencing factor is the quality of the signal processing algorithm. Unfortunately, most brands dont share much information about their algorithm and the expertise of the engineers who designed it.
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The Apple Watch Provides Helpful Though Not Robust Sleep Tracking Along With Its Many Other Features
- Screen type: OLED
- Screen size: 44mm or 40mm
- Battery life: 18 hours
- Fitness tracking? Yes
Apple added sleep tracking to the most recent version of Apple Watch’s operating system, WatchOS 7. Sleep tracking is available on any Apple Watch with WatchOS 7 software, including the Series 6 and the Apple Watch SE. Previously, you needed to download third-party apps to monitor sleep. The standard sleep-tracking feature is very easy to use but not especially detailed. It’s best suited to someone who doesn’t feel they have sleep problems and simply wants to add basic sleep data to Apple Health.
The Apple Watch’s sleep tracking doesn’t provide in-depth data like sleep stages, but does help you keep track of the duration and observe those trends over time. It can also be used in conjunction with other sleep apps on the Apple Watch, which will increase the amount of data available. Outside of this, it’s an effective alarm the Watch’s excellent haptics wake you up with a vibration. It also allows you to set a sleep scheduler to help you stay on track.
Because the tracking is relatively basic, wearing the Apple Watch overnight doesn’t drain much additional battery, but you’ll still have to charge it each day. Wearing it overnight means you’ll have to find a new time of the day to do so.
The Fitbit Versa 3 Is A Reliable Fitness Tracker That Also Monitors Sleep
- Screen type: OLED
- Battery life: 6 days
- Fitness tracking? Yes
The Fitbit Versa 3 is part smartwatch, part fitness tracker. With GPS, a heart-rate sensor, blood-oxygen sensor, and water resistance, it does much more than track sleep. It’s relatively affordable, and Fitbit’s software platform is well regarded.
Fitbit’s sleep tracking works in a similar way across all its devices but varies depending on the sensors inside. The Versa 3 has a heart-rate sensor enabling it to monitor sleep stages, in addition to periods where you’re asleep or awake. It also tracks movement related to disturbed sleep. You need the Fitbit app on your phone to view the data, and it’s available for iOS and Android.
However, one thing to be aware of is that to view some of Fitbit’s deeper sleep statistics you will need a Fitbit Premium subscription. For example, Premium shows average heart rate overnight, how your movement affected your sleep, and further breakdown of the data that makes up your Sleep Score. The subscription also unlocks other features and data sets for daily activity and workouts.
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Physical Health Conditions And Sleep
Using a sleep tracker may help a person identify trends in their sleep behavior, potentially helping them determine ways to prevent nighttime waking.
There are many possible causes of sleep disorders, including some physical conditions that can cause people to wake easily and frequently. People with chronic conditions that cause nighttime waking may find it useful to collect data on their sleep.
Wake After Sleep Onset
One often overlooked but important marker of sleep quality is wake time after sleep onset . It measures how much time you spend awake after having fallen asleep and before you fully wake up. You can calculate WASO using the following formula:
WASO = Time In Bed - Total Sleep Time - Sleep Onset Latency
There are certain conditions that can cause a high WASO, such as sleep apnea, stress, hormone imbalance or a disrupted circadian rhythm.
Depending on your age, a WASO of 30 to 45 minutes seems to be ideal. From experience, I can tell that consuming too few carbohydrates increases my chances of waking up in the middle of the night to use the bathroom, thus increasing my WASO.
Most of the sleep monitors I recommend in this article measure WASO, but some use different terms for it. For example, WHOOP tracks your time awake and uses that to calculate your sleep efficiency, which expresses the percentage of time you spent asleep in comparison to the total amount of time you spent in bed.
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What Can Affect Your Sleep Quality
Your quality of rest can be impacted by many factors, from your environment to your sleep habits. Some common factors include:
Because there are so many different factors that can impact your sleep quality, it can be helpful to use a sleep tracker to identify your sleep patterns and figure out how to improve the quality of your sleep.
Force And Pressure Sensors
Another technique that non-wearable trackers use is force and pressure sensors that detect body movement and even heart rate.
I was highly skeptical of using a sensor under my mattress to detect my heart rate and sleep stages. For example, my experiments with Emfit QS yielded highly inaccurate results. Plus, feedback from others suggests that such sensors often detect sleep when there is a lack of movement caused by inactivity*, such as reading a book.
However, Ive been using the Pod Pro by Eight Sleep and its got built-in pressure sensors to track sleep. Based on the data Ive collected, Eight Sleeps sleep tracking is fairly accurate and in line with what WHOOP, Biostrap and Muse S have reported.
Im still looking forward to what Apple will come up with since they acquired Beddit . I can imagine that paired with a wrist-worn device such as an Apple Watch you can get fairly accurate data, even with low HR sampling from the wrist-worn device.
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The Fitness App Experience
A fitness tracker’s app matters. Whether on your phone or on the web, the app is absolutely vital because it is where you make sense of the information the tracker collects. Fitbit has one of the best apps and websites we’ve tested. It lets you record all kinds of data, such as your weight, menstrual cycles, calories and water consumed, and stress level.
If you want total body analysis, look for a system that incorporates a smart bathroom scale. The Fitbit Aria 2 sends your weight directly to your account, so you can’t cheat the system by entering a lower number. The QardioBase 2 is another top smart scale, especially for pregnant women.
Withings Scanwatch: The Best Sleep Tracker For Sleep Apnea Detection
The Withings ScanWatch is the most detailed and accurate sleep tracker weve used. On top of recording your sleep duration, depth, regularity, and interruptions, it uses its medical-grade SpO2 monitor to detect breathing disturbances overnight. Breathing disturbances are detected when the ScanWatch performs a Respiratory Scan, which measures your heart rate, heart rate variability, respiratory rate, and oxygen saturation levels.
One downside to the ScanWatchs sleep tracking is that it does not monitor your REM sleep stage. Withings said its keeping that functionality exclusive to its sleep mat .
- Small display limits smart features
- Few advanced fitness features or insights
Check out our full review to learn more about the Withings ScanWatch.
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Sleep Trackers Buying Guide
Poor sleep hygiene can be detrimental to your physical and mental health. Sleep interruptions arent only limited to disorders like sleep apnea and insomnia, which are known for causing restlessness at bedtime. Factors like temperature fluctuations, nightmares, light, and noise might prevent you from getting restful sleep.
It might help to use a sleep tracker at night to identify any culprits that affect your overall sleep quality. Its important to note that sleep trackers cannot replace medical treatment or diagnose sleep disorders. However, your doctor might find the data collected by the sleep tracker useful in recommending the right recovery plan to get your physical and mental wellbeing back on track.
How Do Sleep Trackers Work
There are two main kinds of sleep trackers: wearable devices that double as fitness trackers , and standalone no-contact systems that are designed to stay with your bed . Sleep trackers are also available as smartphone apps, but youll find the more advanced technology in the physical products.
At a minimum, sleep trackers track when you fall asleep, when you wake up, and how much time you spend asleep. How are they able to do this?
In the case of wearable sleep trackers, they monitor your sleep using actigraphy. Actigraphy monitors movement through the accelerometer in the wearable device. Just like the accelerometer in your smartphone, its able to sense when youre moving and calculate how many steps you take. If youre lying still for an extended period of time, as one does when youre asleep, the accelerometer notes that lack of movement, and translates it into total sleep time.
Since contact-free sleep trackers are tied to your bed, they cant sense when you start walking around. Instead, these devices rely on infrared technology and movement sensors in the fabric strip to determine when you wake up. They also use ballistocardiography to measure changes in your heart rate.
Many wearable sleep trackers also include heart rate tracking capability. While its primary purpose with those devices is to assess your cardio fitness level, your heart rate does lower as you sleep and changes during the different stages of sleep.
Pod Pro By Eight Sleep
The only device that Ive found to be relatively accurate and reliable is the Pod Pro by Eight Sleep. Its a temperature-controlled smart mattress that has sensors built into its mattress cover. The company calls it the ActiveGrid, and Ive been using it to track my sleep for the past few years.
Based on the comparison data Ive collected, Eight Sleeps tracking capability is more or less in line with WHOOP.
You can learn more about the Pod Pro by Eight Sleep in this article.
If you want to give the Pod Pro a try, you can use the link below and get $150 off the purchase price.
As indicated above, there are several other non-wearable sleep tracking devices on the market but none that Id consider to be accurate.
Still, despite my skepticism and all the negative reviews Ive read of those devices, I ordered the Emfit QS to give it a try.
More Top Sleep Trackers And Apps For 2022
I passed up on several trackers and appslike Withings Sleep and Bedditwhile writing this review, mostly for lack of clinical trials or disheartening findings therein. With that said, I am curious about which apps and trackers you useand which ones you think deserve a second look.
If youre a spanner, how do you quantify your sleep? Do you find that the information is helpful? What did I miss while reviewing all the top sleep trackers and apps for 2022? Let me know in the comments for future article updates!
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Side Effects Of Inaccurate Tracking Devices
The problem with inaccurate sleep trackers is that they might induce stress and anxiety with misleading data and sleep scores.
A few years ago, I had a Jawbone UP wristband that I used to track my sleep. After a few weeks of monitoring my data, I got anxious because of the little deep sleep the device reported: according to the UP, I got only between 20 and 40 minutes of deep sleep every night.
After doing some research, I learned that thats not nearly enough time for the body to recover and go through all its crucial restorative processes . If those readings were correct, I would have felt terrible and exhausted during the day.
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I didnt, which led me to surmise that the device was wildly inaccurate. As a result, I stopped wearing the Jawbone and decided to look for alternative solutions, including apps that would work in combination with the Apple Watch.
While its difficult to determine the accuracy of a sleep tracker without performing validation studies, you can tell if a device is likely unreliable by understanding what sensors and technology it uses.
If youre not interested in the details, you can skip the next section and jump right to my recommendations.
Xiaomi Mi Smart Band 6
At first glance, the Xiaomi Mi Smart Band 6 seems unremarkable, but it comes preloaded with a load of health and fitness applications.
Its design is identical to last years Xiaomi Mi Smart Band 5, with the notable exception of the display, which is brighter and clearer, allowing you to see your daily stats at a glance.
In terms of functionality, you can get all-day stress tracking, a pulse oximeter, and breathing exercises.
The sensors monitors your heart rate, allowing you to fine-tune your fitness settings.
There are, however, a number of disadvantages. The monitoring proved to be somewhat untrustworthy, which is not surprising for a low-cost tracker. When running long distances, you can also keep the band tight to prevent discomfort from friction.
Features and design
Its a mid-range fitness tracker with a lightweight, long, silicone wristband thats almost identical to its predecessor.
With a resolution of 152 x 86 pixels, the screen is very readable. You can pick your favorite face and access your complications with a single tap.
Since it is water-resistant to 50 meters, it is not recommended that you wear this watch while swimming or snorkeling. At most, light rain showers.
The Xiaomi Smart Band 6 has a few more capabilities often associated with a more expensive wearable. Stress management, breathing techniques, and female cycle monitoring are all part of this.
The Mi Smart Band 6 reliably measures deep and light sleep cycles, as well as REM sleep cycles.
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