What Sleep Tracking Apps May and May Not Tell You

Activity trackers and sleep tracking apps will happily provide you with statistics on your sleep: how many hours you were in the bag, for example, and whether the sleep was good “quality”. But you cannot take these numbers at face value, and some of them are completely wrong.

Sleep trackers don’t actually analyze your sleep (even though they say what they are doing)

We spoke with Dr. W. Christopher Winter , a specialist in sleep medicine and neurology and author of The Sleep Solution . Dr. Winter previously brought Fitbit, Jawbone, and phone trackers to his sleep lab and strapped them all to his arm . All devices could tell when he went to bed and when he woke up, but none of them could reliably distinguish different stages of sleep (for example, REM sleep or sleep in sleep) from each other.

Wearable devices track sleep by motion, just like apps like Sleep Cycle and Sleep as Android , either by detecting bed movement or listening to sounds at night.

Movement is not the same as sleep, Dr. Winter emphasizes, but sleep laboratories track movement – along with other bodily functions such as breathing, eye movement, and brain activity.

So you can ignore the number FitBit gives you for “sleep efficiency”, or “Sleep as Android’s opinion” for how much time you spent in “light” rather than “deep” sleep. There is no way for them to get a complete picture of when you actually sleep or what stage of sleep you were in.

It is also normal to move during sleep and wake up several times during the night. We usually don’t remember these movements or awakenings. So if you see them on the output of your sleep tracker, don’t worry. As long as you feel well rested in the morning, movement is not a problem.

Sleep trackers are great for identifying patterns over time

On the other hand, the difference between apps and trackers lies in their ability to provide you with big data. “It is very difficult to get polysomnography data in 30 days in the laboratory,” says Dr. Winter, but during this time it is easy to put on the FitBit or sleep next to the phone.

If you are worried about not getting enough sleep, a tracker can help you figure out if this is true. Dr. Winter told us the story of a lawyer who was convinced she never slept more than an hour a day, but her FitBit recorded six hours. She thought FitBit was broken. Laboratory research showed that this was correct: she slept much more than she expected.

On the other hand, Dr. Winter decided to track his sleep and found that he went to bed later than he thought. “He told me very bluntly, ‘Hey dude, you tell everyone you sleep 7 hours, you’re a fucking liar, on average you only have 6 hours and 15 minutes.’ It’s not enough. ”Now he makes more efforts to go to bed on time, instead of being distracted by nightly chores and television.

Sleep tracking can also help you spot patterns when things change in your life: if you start a new job or exercise, a sleep tracker can help you make sure you are still getting enough sleep. Likewise, certain medications can make your sleep more restless and your app will report more wakes or movements during the night so you can see if there is a problem. If you feel sleepy during the day, this data can help you figure out the cause.

Experiment with yourself and focus on the big picture

Dr. Winter offers another benefit of sleep trackers: they allow you to test for yourself what is really affecting your sleep and what is not.

If you don’t believe alcohol can harm your sleep , you can compare how you sleep at night when you drink a lot to nights you don’t drink and see for yourself. Or, if you can’t put your phone down in the evenings , try it for a week and see if your sleep improves.

But if you don’t have a specific question or concern about your sleep, it may be best to ignore your sleep data for now, and there is little reason to invest in a sleep tracker “just because”. The fact that a number can be measured does not mean that it is a number to worry about, or even medically useful. Use the sleep tracker as a tool for solving problems or questions you may have, not as an all-knowing judge about whether you are “sleeping properly”.

Illustration by Angelica Alzona .

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