How Do Smartwatches Track Sleep

How Do Smartwatches Track Sleep?

If you’re a smartwatch owner or a fitness tracker owner, you know that your device can track your sleep. It notes what time you nod off and wake up, it knows when you’re tossing and turning, and when the silent alarm rouses you in the morning, all of your data is right there on a screen for you to scrutinise. You know how long you’ve slept and if it was relatively restful, and if you possess any competitiveness in you whatsoever, you’re determined to get a better night’s sleep tonight. But how do smartwatches track sleep?

How Do Smartwatches Track Sleep?

How Do Smartwatches Track Sleep?Your smartwatch tracking your sleep may seem like magic, but of course we know it’s thanks to big advancements in wearable technology called actigraphy, or the practice of measuring gross motor activity through non-invasive methods to track sleep.

It relies on a tri-axis accelerometer, which monitors your movements and can tell with relatively good accuracy if you’re awake or asleep. Most smartwatches have heart rate monitors as well, which helps with sleep tracking accuracy.

The sleep tracking function on smartwatches doesn’t really gather information on deep REM sleep versus light, fitful sleep; to get that sort of information, you’ll need to measure brain waves, eye movement, and several breathing metrics.

Still, using a smartwatch to track your sleep will give you a good idea of how much shut eye you get at night and just how restful it is.

But is it Accurate?

The short answer is yes, smartwatch sleep tracking is mostly accurate, and a 2015 study confirmed this. In the experiment, the researchers compared the accuracy of a fitness tracker’s sleep tracking accuracy with that of polysomnography, or a full sleep clinic test that measures things like brain waves, blood oxygen levels, and other particulars.

The conclusion they reached was that the wearable tracker’s data was mostly aligned with that of the more in-depth, time consuming, and expensive test.

Granted, the fitness tracker in this study was a Jawbone UP and not a more well appointed smartwatch, but it’s important to remember that the Jawbone used by the researchers uses an accelerometer just like the one found in any smartwatch. The outer packages may be different, but the technology under the hoods is the same.

It should be emphasised, though, that smartwatches aren’t a medical device. They’re meant for casual self assessment, and are never a replacement for the advice of a doctor or the analysis of a sleep clinic.

Again, the sleep tracking function in smartwatches measures movement and maybe heart rate. It doesn’t measure brain waves, which are needed to determine sleep stages and render fully accurate sleep information. Ultimately, smartwatches, while highly advanced tech-wise, are still consumer products.

If you have serious concerns about your sleep, consult your doctor and not your app.

An Important Drawback

The biggest disadvantage with smartwatch sleep tracking isn’t a matter of technology, but a matter of timing. The batteries that power many smartwatches last for maybe a day or two before needing a charge, and many smartwatch owners charge their devices at night. As this article from Forbes points out, you can’t track your sleep and charge your smartwatch at the same time.

If you want to use your smartwatch to track your sleep, you’ll probably need to adjust your charging schedule a little and make some accommodations. Perhaps you can charge your device right when you wake up, while you’re getting ready for your day, or even for a few hours before you go to bed.

It’s an issue that can be resolved, of course, but not without a little thinking ahead. So, the bigger answer to the question, “How do smartwatches track sleep?” may be, “With careful planning.”

Is Sleep Tracking Necessary?

We track so much these days that sooner or later, we need to ask ourselves why we’re doing it. Really, we usually don’t need a device to tell us that we don’t get a good night’s sleep — we feel groggy and irritable and know that it’s because we didn’t get a good night’s rest. The numbers on the smartwatch screen in the morning aren’t providing much new insight.

However, some smartwatch and sleep tracker owners insist that just like wearing a fitness tracker encourages us to pay more attention to our activity and get more of it, wearing a smartwatch or other sleep tracker encourages us to go to sleep at a more reasonable hour and to be more mindful of allowing our bodies to truly rest. We’re motivated by the good numbers: we like seeing that we’ve done something well.

We like patting ourselves on the back for walking 10,000 steps in a day or sleeping eight hours in a night. What’s more, these are small goals that we can achieve as long as we’re conscious of them.

Yes, we have to play these silly psychological games with ourselves, but this may be a case of the ends justifying the means: if we wear a smartwatch to bed, we’ll try harder to sleep better.

What do you think? Do you use your smartwatch for sleep tracking? Does it seem to be accurate? And when do you charge your device? Leave a comment and tell us about your experience.

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  1. O

    Good article. Thank you for taking the time to write it and research for it. I wear my Pebble 2 smart watch to sleep and it seems accurate. It knows the time I fall asleep and wake up. When I get a bad nights sleep I have the evidence on my wrist to show anyone who may have caused it lol. I charge the watch while I shower because I don’t want it to confuse me washing my hair with taking steps. It charges very quickly and a full battery last 4-5 days so charging it every other day or so while showering has been working out for me. I just wish it didn’t innaccurately tracks steps while I sleep. Tossing and turning ends up displaying as a couple hundred steps.


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