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Fitness trackers 101: How do fitness trackers track sleep?

Fitness trackers 101 How do fitness trackers track sleep
Latest Update: May 4, 2018

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One feature of a sleep tracker to evaluate the general health of a person is the sleep monitor which monitors the quality of sleep by monitoring your movements and translating them into sleep data.  You see a detailed report, usually a graph, which tells how well you sleep at night. But how do fitness trackers track sleep?

Fitness trackers generally monitor the number of steps you have covered throughout the day and the calories you’ve burned, but this article will only discuss the mechanisms and processes how fitness trackers track sleep. Is the data they provide accurate enough to tell your sleep quality?

How do fitness trackers track sleep? Accelerometers

Fitness trackers measure sleep with the use of accelerometers, a group of sensors that detect a user’s motions, including the direction and speed of each motion. However, sleep professionals and researchers warn about putting too much trust in these sensors. It is true that they can tell whether the user is asleep or awake but they are also liable to mistakes.


Another significant term that defines how fitness trackers track sleep is actigraphy. Actigraphy is a method of utilizing a device to monitor movements to identify the amount of sleep. When you turn on the “sleep mode” of the sleep tracker, it starts monitoring your movements.

The next morning you’ll be able to see your sleep data as the device translated these movements. You will have an idea how this works when you try to edit your sleep times. Your movements during the times you were awake are reanalyzed when you tell the software that you were really asleep.

Actigraphy is done with the use of an actigraph wrist-worn device that monitors your movements while sleeping. It is usually worn at home, and does not feel uncomfortable. It has software that interprets the movements into moments of wakefulness and being asleep. This actigraph device is usually recommended to people with sleep disorders because it is a more convenient way to track sleep patterns rather than sleeping in a lab where doctors can study their sleep. It is worn 24 hours a day, 7 days a week to monitor sleep based on movements.


The general, most accurate way to track sleep is the polysomnography or PSG. It requires the person to sleep in a lab where brain waves are examined by an EEG. In an EEG, electrodes attached to the scalp measure the waves of your brain. It is inconvenient but experts prefer it because it is accurate. PSG is the standard of actigraphy. It is used to compare the accuracy of actigraphy.

Can fitness trackers determine sleep stages?

Some researchers are doubtful about the accuracy of actigraphy. Can it track sleep stages? Actigraphy devices depend on movements; hence they can’t determine sleep stages. Experts instead conduct EEGs to measure a patient’s brain waves and identify the different stages of sleep. An EEG also monitors eye movements and muscle tone to measure random eye movement (REM) sleep.

Possible threats of sleeping data inaccuracy

For those who do not have a sleeping disorder, the sleep tracking function of fitness trackers won’t affect them. But this is another thing for someone with a sleep disorder; this device might give them inaccurate data. The sleep trackers might say that you have 8 hours of sleep and you would think that you don’t have a problem.

But what if the person really has a sleep problem? Undetected sleep disorders can pose possible threats to you and/or to people around you. You might drive while not alert due to lack of sleep, which might cause an accident on the road.

In addition, accelerometers or actigraphy won’t provide enough data for identifying the quality of sleep. People with sleep apnea, for instance, may cease their breathing hundreds of times during their sleep, and this condition can’t be detected by a fitness tracker.


Fitness trackers are wearable devices worn day and night to monitor the distance walked or run, calories burned, the heart rate, and other fitness related metrics. They come in different styles such as smartwatches and wrist watches paired with phones or computers.

Even though they might provide inaccurate data, the sleep monitoring function of fitness trackers are still helpful. It makes people aware of possible sleep disorders and general health conditions through sleep quality. However, people with possible sleep disorders should consult specialist doctors or appropriate sleep laboratories for a more accurate diagnosis.

Date Published: November 13, 2017

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