Sleep trackers are electronics that take in data to find out when and how much you are sleeping. They automatically do what keeping an old-fashioned sleep log does but with additional data you cannot gather while unconscious.

People wonder, “How do sleep trackers work?” and sometimes conclude that they can’t possibly know when you are actually asleep. Some sleep trackers are reasonably accurate, but you should take their data with a grain of salt in order to make the smartest choices about your sleep habits.

How do sleep trackers work? 

Sleep trackers rely on data that they collect from the movements you make, your heart rate and breathing patterns. They record this combination of data and create a graph that shows things like your total length of sleep, any times of wakefulness and when those times occurred. 

Some trackers will integrate room data as well, such as temperature, humidity, light and noise, helping you see whether those factors change the sleep you get. The more information the sleep tracker can take in, whether through automatically sensing that you have gone to bed or because you activate the sensor, the more data it can give you in the morning about how you slept.

How do sleep trackers know you’re asleep?

Sleep trackers focus mostly on movement through an accelerometer, the same technology that lets a fitness tracker note when you are taking steps. Unfortunately, this isn’t a perfect gauge for sleep since you can be still while awake, and some phases of sleep include minor movements that could be tracked as waking up.

While new data sensing technology is used all the time, most sleep tracking cannot measure brain waves how a polysomnography sleep study will, which is one of the most reliable ways to gather information about your sleep stages.

As sleep tracker technology has progressed, this information is incorporated with heart rate tracking to get more accurate data when you are asleep and awake. Other sleep trackers use what scientists have estimated about sleep stages to approximate how much time you are spending in each stage. 

Do sleep trackers work, really? 

Sleep trackers generally are tracking something, so in that sense, we do know how sleep trackers work, but whether the data you gather is useful or not depends on what you’re trying to do. For instance, science researchers found that commercial wearables were more useful for good sleepers than those with insomnia. One particularly advanced tracker, the OURA ring, was featured in a scientific study showing to yield some similar data to a traditional sleep study using polysomnography.

Here are three takes on whether sleep trackers work: 

Tom Briechle on Fitbit’s Sleep Stages 

In Men’s Journal, Tom Briechle praised Fitbit’s interface that shows wake time, REM sleep, light sleep, and deep sleep. He was able to note how sleep trackers work and the features he valued. He liked that you don’t have to activate it; rather, it senses on its own that you are attempting sleep. He noted that the app occasionally caught a half-hour more sleep than he actually got from when he spent lying on a couch in the morning looking at social media.

Christen Costa and Beddit

Gadget Review considered a different kind of sleep tracker, the Beddit. This tracker adheres a strip to your mattress rather than requiring you to wear a band for sleep. Reviews were mentioned as seeing the sleep tracker detach from the mattress, but otherwise, it was very easy to use. It also provides readouts on heart rate, sleep cycles and suggestions for what to consider changing in one’s sleep.

Jeremy Horwitz and Apple Watch’s Sleep Tracking Feature

Venture Beat discusses the widespread Apple Watch sleep tracking feature, particularly noting that you don’t want it running and eating up battery life if you aren’t using it. He was disappointed with the simple insights gleaned, basically just “time in bed” versus “time actually asleep,” with some heart rate data available but hard to find. He concluded that this app might get more development over time.

Types of Sleep trackers

Wearable Sleep Trackers

The most common sleep tracking currently is the sleep tracking application within a wearable smartwatch or other tracking device attached to you. These trackers use the data taken while you are asleep through contact with your body and usually display the results in a phone app, given the small screens on smartwatches.

Bedside Sleep Trackers

A bedside sleep tracker tracks movement and possibly the sound of your breathing and keeps the data. These are considered a good option for those who find a smartwatch restrictive or distracting while sleeping. While a few of these devices have entered the market in the past ten years, they haven’t caught on as much as wearables and newer mattress sensors have.

Mattress Sensing Sleep Trackers

A new kind of no-contact sleep tracker option is the sensor that goes either under your mattress, in your sheets, or somewhere else in contact with your bed. This gives you more accurate movement data in some cases than a full bedside tracker, but without the constriction of wearing a fitness tracker or smartwatch during sleep. Another form of a sensor is a smart pillow or smart mattress, which integrates the sensor into the sleep accessory.

Final Thoughts

Fitness tracking and sleep tracking are helpful in similar ways, in that they help to motivate good habits and push us to get more sleep or more exercise. However, suppose you hope to use a sleep tracker to analyze more complex data, such as whether you have a sleep-related disorder or are not getting deep sleep. In that case, you may be better off commissioning a sleep study since the data taken during those studies are more complex and focused on brain waves rather than the less-informative data that a smartwatch or bedside sleep tracker can give.