How do watches track sleep?

Last Updated on September 24, 2022 by Luis Cooper

When you close your eyes, your ability to move around is limited.

But there is a solution that could be closer than you think: smartwatches.

They’re the latest accessory for any night owl who needs to know how much sleep they’re getting.

Smartwatches track and record everything from how much sleep you’re getting to whether or not you snore.

Inside, a smartwatch has a heart rate monitor, accelerometer, gyroscope, and magnetometer.

Together, these sensors let the wearable device sense movement, then wake the wearer up with a gentle buzz.

In this article, we will discuss the How do watches track sleep?

What is a Wearable Fitness Tracker?

A fitness tracker is a device worn on the wrist or around the waist that monitors specific bodily functions, like movement and heart rate.

Today’s market offers a variety of innovative fitness trackers that can connect to a smartphone or a laptop.

Most have three-axis accelerometers, allowing them to track how quickly a person moves in any direction.

Calculated algorithms are then used to process this data to understand the movements better.

How Does a Fitness Tracker Work to Track the Sleep?

Most contemporary fitness trackers are worn by the user around the waist or on the wrist in place of a watch.

The tracker’s sensors maintain track of all the input they receive.

The paired fitness tracker’s smartphone or laptop gets this info after that.

When the device is connected to a computer or smartphone, this occurs.

Using complex algorithms, the software organizes the data it has gathered into knowledge that the user will comprehend.

It enables the individual to keep an eye on their heart rates, levels of activity, and even their sleeping habits throughout the day.

Trends can be found based on the history of the data that is available for the individual.

This information is then delivered to the individual so they may view it and make a more informed decision about their exercise schedule.

Is it worth wearing your fitness tracker to bed at night to track your sleep?

Have you ever thought about how your fitness tracker records your sleep?

Or perhaps more crucial, does it accurately record data?

Every fitness device on the market, including Fitbit, smartwatches, Garmin, and countless others, functions similarly.

Wearing a fitness tracker is not likely to be a trustworthy predictor of your sleep health if you have or if your sleep is frequently disturbed.

An in-home sleep study is the best alternative to obtain a reliable and precise reading.

The majority of smartwatches and fitness trackers contain what is known as a tri-axis accelerometer.

That’s a technical way of explaining that your wearable has an accelerator.

It is a tiny gadget with axis-based motion detection that monitors motion in all directions.

Some even have a gyroscope built-in to detect rotation and orientation.

Your tracker converts the motions of your wrist into sleep patterns using an actigraphy technique.

As you may imagine, it’s not always precise, and some guesswork is involved.

It is so because actigraphy only records movement.

And observing sleep involves much more than merely tossing and turning.

Monitoring brainwaves, eye movements, and respiration are necessary to distinguish between deep REM sleep and light sleep.

A study on the effect of fitness trackers on sleep was published in the Journal of Clinical Sleep Medicine by psychologist Kelly Glazer Baron, Ph.D., MPH, of the Rush University Medical Center.

According to Baron, a portion of the issue is caused by the technology itself.

According to Baron’s assessment, these increasingly common devices “are unable to discern stages of sleep,” citing numerous studies effectively.

They are unable to distinguish between light and deep sleep, as Baron explains.

They might call it to rest while you’re studying on the couch.”

While reliability is questionable, trackers can be a helpful guide.

Numerous research has produced inconsistent findings on the dependability of fitness trackers.

Still, the general view is that actigraphy is generally reliable enough to monitor sleep in healthy adults with typical sleep patterns.

I said it’s less accurate.

Well, psychology is the key to it all.

When your fitness tracker indicates that you slept for eight hours, you could pat yourself on the back (regardless of how accurate it is).

And that’s advantageous.

Tracking anything connected to your health was well recognized to increase your awareness of your options even before wearable technology was created.

You typically take more steps when counting your steps.

Sleep tracking can also help you stick to your health goals or resolutions.

Tracking provides you with small daily goals for better health instead of just concentrating on a significant health goal, like reducing 20 kilograms.

Setting smaller, more manageable goals makes you feel more accomplished.

On the other side, if you have a predisposition toward perfectionism, failing to get the recommended 8 hours of sleep could make you more anxious, which will impact your rest.

According to Baron, those obsessed with the “quantified self” rely on daily data collection to improve their emotional and physical well-being.

“Some people take it too far, and that can be stressful,” the speaker continues.

The science behind wearable sleep trackers:

Actigraphy is one of the primary measurement techniques used by wearable sleep monitors.

Actigraphy mainly entails capturing movement using an accelerometer as a measuring tool.

The theory is that you are awake when you move about a certain amount, and when you are stationary for extended durations, you are asleep.

Why actigraphy can be useful:

Sleep specialists have used actigraphy to measure sleep for many years.

Even though polysomnography is the industry standard for measuring sleep, actigraphy has a significant impact, especially since polysomnography has several drawbacks.

It makes sense that a patient in a lab rather than their bed, linked to various devices, with multiple electrodes stuck to their head, could not sleep usually.

Actigraphy is, therefore, less expensive than polysomnography.

It allows users to wear a sleep device at home for a week or two, providing a more accurate picture of their sleep patterns than just one or two clinic nights.

What can wrist actigraphy reliably tell you about your sleep, and how accurate is it?

Fortunately, those two issues have generated a good deal of research.

Should you trust it? (How do watches track sleep?)

What does this mean, then? Do you believe your fitness tracker can accurately detect when you are sleeping or not?

I don’t have any expertise in sleep.

Still, based on what sleep scientists are saying and the findings of actigraphy studies, it appears safe to use it as a general indicator of your sleep time and efficiency as long as you usually get good sleep.

Do not trust actigraphy if you have (or suspect that you have) a sleep issue.

In that circumstance, a PSG test at a sleep clinic is essential.

I haven’t yet encountered a sleep researcher willing to attest to the accuracy of sleep phase prediction based on movement alone for various sleep phases like deep sleep and REM sleep.

As a result, it would seem that we should base our decisions on the total amount of time spent sleeping rather than the purported sleep phases that our trackers purport to be measuring.

The limitations of actigraphy:

The idea that sleep trackers work best when you get moderately good sleep has been brought up in numerous internet pieces where the writer has consulted sleep specialists.

Errors only really stand out when your sleep has been disturbed.

And it appears that other sleep lab owners share their skepticism because research supports their claims.

Sleep researchers compare sleep trackers with polysomnograms:

Many people probably want to know how big the elephant in the room is, but we don’t have any tools for measuring elephants.

Additionally, no authority overseeing sleep trackers assists us.

However, a small number of studies comparing sleep trackers with polysomnograms, EEG, or sleep diaries have been conducted recently.

Even so, they are worth thinking about because they contain particular recurring everyday discoveries.


Short answer: 

It cannot distinguish between light and deep sleep.

Tri-axis accelerometer and a heart rate monitor are features of the smartwatch (the one that sits on the back of the watch with red or green light).

They utilize an algorithm with this technology to ascertain whether you are awake or asleep.

However, it cannot monitor the caliber of your sleep because measuring eye and brain activity is required to obtain this information.

Your tracker converts the motions of your wrist into sleep patterns using an actigraphy technique.

And observing sleep involves much more than merely tossing and turning.

Monitoring brainwaves, eye movements, and respiration are necessary to distinguish between deep REM sleep and light sleep.

If you have any questions, please ask in the comments below.

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Hi, I'm Luis, the guy behind this site. I love wearing watches, especially ones that look great on small wrists (mine are about 6.3" around). The Watches Geek is dedicated to helping you learn about and buy watches that you will love wearing. I want this website to be the last destination for people to pick the best watches to fit their needs. You can find our unbiased reviews here on Thewatchesgeek.

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