The Truth About Sleep Trackers


Sleep is big business, which is most wrist-worn wearables now track sleep. And it’s part of why Apple recently released the $150 Beddit Sleep Monitor 3.5, a companion to the Apple Watch which requires nightly charging, making it suboptimal for sleep tracking.

Beddit Sleep Monitor 3.5 via The Vergge

Beddit Sleep Monitor 3.5 via The Vergge

Consumer sleep-trackers aren’t very accurate

Sleep scientists use polysomnography to measure sleep in sleep studies. Polysomnography is a comprehensive test that combines an EEG with other body change monitors to measure brain waves, eye movements, heart rate, breathing patterns, blood oxygen levels, body position, chest and abdominal movement, limb movement, and noises (such as snoring, talking, etc.).

Multiple studies have shown that sleep trackers are less accurate than polysomnography, consistently overestimating sleep efficiency and total sleep time.

"Most consumers are unaware that the claims of these devices often outweigh the science to support them as devices to measure and improve sleep," authors of a 2017 study of the accuracy of wearable sleep tracking devices warned.

Neurologist Dr. Lev Grinman told NY Mag that most sleep-tracking tech “isn’t necessarily what a sleep physician would use to gauge how well somebody is sleeping,” Dr. Grinman said. “Everybody wants the do-it-yourself kind of thing. A lot of these things are geared toward just the general consumer. Even though they say they’re backed by sleep science, they’re not robustly accurate.”

I recently spoke with Dr. Charles Samuels, a sleep physician and the Medical Director at the Centre for Sleep and Human Performance for the Does It Work? Podcast. Dr. Samuels has been studying sleep for more than 15 years and is currently working with Red Bull to study the impact of sleep on Esports athletes (video game players).Dr. Samuels developed the Athlete Sleep Screening Questionnaire (ASSQ), which a 2015 study published in the British Journal of Sleep Medicine found is more accurate than the standard psychometric sleep survey when it comes to finding sleep disturbances in elite athletes.

“I’ve been now to two international meetings discussing the use of technology and sleep analysis,” Dr. Samuels told me. The consensus was that when it comes to consumer sleep trackers, “it’s very unreliable information.”

Problem 1: Movement isn’t sleep

Most sleep trackers use accelerometers to track movement, not sleep. Wearables work on the assumption that movement equals wakefulness. “And sleep is inferred from there,” Dr. Samuels said.

That’s probably true for most people. Some sleep disorders like Restless Legs Syndrome and

Periodic Limb Movement Disorder cause troublesome movements that disturb sleep. However, some people just move a lot in their sleep, so not all sleep movement indicates a problem.

To get around this limitation, some devices combine heart rate with movement to track sleep, including the Beddit Sleep Monitor 3.5. It lives between users’ mattress and sheets and measures sleep time, heart rate, breathing, snoring, bedroom temperature, and humidity.

While it’s likely more comfortable than any worn sleep tracking device, Ars Technica points out that it won’t be able to track people who move while they sleep as closely as those who stay still because it won’t stay next to your body like a wristband.

“We’re very cautious about their use,” Dr. Samuels said. “The biological validity of that data is very low.” Transparency is also very low. Consumer Reports warns about the troubling opacity in devices’ sleep-tracking algorithms.

Problem 2: Sleep trackers can hurt your sleep

“We have patients who come in and say, ‘Oh, look at my app’ and whatnot,” Dr. Samuels said. “If a person has a sleep problem, that device is completely useless. If someone says, ‘I sleep poorly so I’m going to use an app to track my sleep,’ that’s not very helpful. If it’s helping them sleep better, fine. But if it isn’t, we tell them to stop. Because they can be more destructive than helpful, actually.”

Consumer Reports warns that sleep trackers can reinforce bad sleep habits by encouraging users to spend more time in bed.

And sleep researchers warn that sleep trackers “may reinforce sleep-related anxiety or perfectionism for some patients.”

“People believe it when they see it in a picture,” Dr. Samuels said. “And of course that’s the marketing of these devices, to make it pretty and then people believe it. The reality is it’s not very valid. There’s a whole discussion around that from a scientific perspective. We use those devices in research, so we know how they work. And we know how valid and reliable they are.”

“Now if it’s helping them sleep better, great,” Dr. Samuels said. “But that’s not science, that’s not evidence, that’s just an anecdotal experience. And I don’t work on that platform at all.”

Even though sleep trackers not as accurate as EEG or polysomnography, they’re still useful for measuring changes in your sleep patterns.

If you start using an advanced sleep-tracking device today you’ll be able to see whether your lifestyle changes impact your sleep duration and quality.

When combined with a sleep journal, advanced sleep tracking can provide insights into how different kinds of sleep impact your mental and physical performance.

Here’s an example of a sleep journal:

sleep journal.png

If you’d like to start tracking your sleep with a sleep tracking device plus an automated sleep journal, download the Biomarker app here.

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Cathy Reisenwitz