How Sleep Trackers Work

This content was created by the National Sleep Foundation

Find out how these digital devices spy on you while you snooze.

You might think that if you got eight hours of sleep last night, you're golden. But that's not necessarily the case. So much more goes into measuring a successful night of zzz’s than just the number of hours that you have your eyes closed. In other words, it's not just about quantity of sleep—it's also about quality of sleep. Other important measures that affect how well you sleep, for example, include how often you toss and turn, how many times you wake up during the night, how many cycles of sleep you get, and more.

A bunch of new digital devices on the market are claiming to help you better understand these factors, so you can get a sharper picture of the quality of sleep that you're getting. But, how, exactly, are they measuring this?

Enter: The Accelerometer

Most sleep trackers measure your sleep quantity and quality using something called an accelerometer (otherwise known as a small motion detector). The accelerometer is part of one approach to sleep research known as actigraphy, which measures one metric of sleep—your movement—rather than measuring multiple variables at once.

Sleep quality has traditionally been tested using an approach called polysomnography, which involves going to a lab and having over 20 wires attached to you while you snooze. This tactic measures breathing, heart rate, eye movement, and more.

Which is more accurate? The jury is still out. Some experts claim that actigraphy isn't quite as accurate, since it measures only a fraction of what polysomnography measures. But others argue that even if polysomnography measurements are more accurate, people aren't likely to sleep the way that they normally do when they're in a lab, rather than their own beds.

The bottom line: If you're considering using a one, read about the latest sleep trackers to see which kind suits you best and interpret any readings that you get with a grain of salt.