How Does A Fitness Tracker Track Sleep

Fitness trackers are devices that monitor a number of different parameters such as steps taken, heart rate, calorie intake, calories burned, sleep and so on. They come in various sizes and features.

How does a fitness tracker track sleep
Photo Credits: Daria Shevtsova,

We spend close to one-third of our lives sleeping, and the quality and amount of sleep we have to play a big role in the other aspects of our lives. So, it doesn’t come as a surprise when you are eager to know the number of hours you sleep every day. 

People also want to find out if they are getting enough good sleep devoid of any sleep disorders to tackle. There is a general awareness of the need to track sleep. 

Before now, there was virtually no means of tracking your sleep. There were very few options available.

You can’t possibly keep a record of your sleeping patterns while you are asleep except you ask your someone to tell you. Of course, even if it is possible you won’t get an accurate result. 

One other way to track your sleeping pattern accurately is to spend one night or more in a specialist hospital. Well, there is a more convenient and better way to track your sleeping patterns accurately; getting a fitness tracker that can track sleep.

Even though scientists are still debating about their sleep tracking accuracy, we are sure that these tiny little devices can tell when you are awake or asleep.

Maybe you have wondered in the past, how does a fitness tracker track sleep? In this article, we are going to look at the mechanisms involved in sleep tracking and all you need to know about this activity tracker.

If you prefer learning by video, this article is also explained here.

Withings Sleep - Sleep Tracking Pad Under The Mattress with Sleep Cycle Analysis

Buy this Withings Sleep Tracking Pad on Amazon

What Does A Sleep Tracker Monitor?

Video: What Does A Sleep Tracker Monitor?

Watch this video to know everything sleep trackers monitors.

There are several fitness trackers that can monitor sleep patterns. While most of them are worn on the wrist, others are kept on your bedside table or attached to your pillow. 

Most sleep trackers have common features like knowing when you are sleeping or the duration of your sleep. Sleep trackers monitor your sleep in the following ways:

Duration of Sleep

Sleep trackers monitor and evaluate when you sleep and when you wake up. This way it records the total time spent sleeping. This determines if you are having enough sleep or not and helps you to make the necessary adjustments. 

Stages or Phases of Sleep

Certain sleep tracker model monitors your sleep phases or stages. That is whether you are sleeping lightly or deeply. And so, set off an alarm to wake you during a phase when you are not sleeping deeply. This makes it easy for you to wake up. 

Quality of Sleep

They are designed in such a way that they can identify any movement or disturbance during your sleep like waking up, turning, tossing and so on. They do that to know if your sleep was restless or restful.

The Environment

Sleep trackers evaluate or record environmental factors that can affect your sleep patterns like temperature, or light in the bedroom. After gathering this data, it can tell you if you will get enough sleep in that environment or not.


A lot of factors from your daily activities can really affect your sleep. Some of these factors are exercise, diet, caffeine intake and so on. It also monitors all physical activities you engage in like stress level, heart rate, and food consumption.

This is to enable it to evaluate how your daily activities may affect your sleep patterns and helps you change your lifestyle.

Beautyrest Sleeptracker Monitor – Wearable-Free Sleep Tracker – Intuitive App and Alexa Enabled

Buy this Beautyrest Sleeptracker Monitor on Amazon

Sleep Cycle

There are four different stages or phases of sleep in a typical sleep cycle, these are:

Stage One – Non-Rapid Eye Movement Sleep (Non-Rem)

This is the first stage of sleep which lasts for a few minutes. It is light and easy to rouse from with brain waves of slow wavelength. During this phase of sleep, muscle tone relaxes, and eye movement slows down. The brain waves start to slow likewise.

Stage Two

This stage of sleep is also light like the Non-Rem sleep in stage one. During this phase of sleep, the eyes stop rolling. Brain waves keep slowing down but experience unique bursts of activity known as the sleep spindles. They also exhibit sleep structures known as ‘K’ complexes.

Stage Three – Deep Sleep

This stage of sleep is characterized by a state of deep sleep that is difficult to rouse from. It is in this stage that body growth, repairs, and immune system boost occur. This stage is also called the slow-wave sleep as the brain waves slow down rapidly to delta waves.

Stage Four – Rapid Eye Movement (REM)

This is the final stage of the sleep cycle. During this stage, the brain is more active and processes information and stores them in long-term memory. Dreams also occur in this stage and your eyes move from side to side.


The sleep cycle repeats every 90-110 minutes every night and as sleep continues, rapid eye movement sleep increases in length.

Buy this Lintelek Fitness Tracker With Sleep Monitor on Amazon

How A Sleep Tracker Can Know You Are Asleep?

The major way a sleep tracker know you are asleep is via your body motion or movement. We are quieter or still when sleeping than when we are awake except for the occasional turning and tossing. Hence, body movement is a good factor for monitoring sleep and arousal.

The process of monitoring body movement and sleep patterns is called actigraphy or accelerometry.  Wearable fitness trackers that track sleep use a sensor called the actigraph sensor which is worn on the wrist.

Whereas, most smartphone fitness tracking applications uses the phone’s 3-axis accelerator to track body movement.

Most wearable fitness trackers that monitor sleep come with a setting on the gadget called the ‘Sleep Mode’. It is activated by the user and data is recorded from the time you slept to the time you woke up.

Also, a sleep tracker uses both environmental and personal factors to know if you are sleeping or not. These factors include:


A few sleep trackers have a thermostat feature that monitors your room temperature to determine its effect on the quality of sleep. The perfect temperature for sleep is below 60oF for adults, and a little warmer for children.

If the sleep tracker notices a temperature outside this range, it might suggest that you adjust the thermostat for better sleep. 


Some models may have a special built-in microphone that is used to catch noise or sound from your body or room. The presence or lack of noise or sound helps the sleep tracker to know if you are sleeping. 

It also helps it to determine your sleep quality. The microphone inside the sleep tracker may measure respiration to identify any form of snoring. This can obstruct sleep quality. 

A few sleep trackers may also record snoring to determine if it is just snoring or you are gasping or making some choking sounds. This may suggest a severe sleep disorder. For example, sleep apnea.

Sometimes, the microphone can catch some ambient noise. This will help you check if your bedroom is suitable to sleep in. If your bedroom is so noisy as a result of sounds from television.

For example, the sleep tracker can suggest that you move away from the noise because it might disrupt your sleep.


A dark and quiet room is a perfect environment to sleep.

Heart Rate

A Sleep tracker has the capacity to measure your heart rate, the variations of your heart rates or the lack of it. It uses this to determine when you are awake or sleeping and makes a well-detailed estimation of when you are in the rapid eye movement sleep (REM). 

When you are sleeping, blood pressure lowers, and heart rate reduces. Heart rate remains fairly steady throughout the duration of sleep except during rapid eye movement sleep. In this stage of sleep, you may encounter an increase or variations in heart rate when you wake up.

A wearable sleep tracker uses a heart rate monitor (HRM) technology to monitor heart rate. It uses a heart rate sensor that is attached to the skin or body.

Another way to measure heart rate is by monitoring the continual movement or motion of the body using a mattress sleep tracker. The mattress sleep tracker uses a ballistocardiography (BCG).

The strip found in the mattress sleep tracker has the ballistocardiography sensor, to track how the body movement or motion affects the movement of the mattress strip.

Movement Sensors

Certain sleep trackers don’t use the actigraphy sensor at all. This is because they are not worn by the user or attached to the mattress. These models look for a means to monitor movement without attachment to the body.

They sit on the nightstand in the bedroom. It monitors if you are sleeping or awake by using environmental factors such as temperature and light. These factors can identify when your bedtime draws near. 

Also, they will rely on movement sensors to monitor the time you enter your bedroom and when all movement ends in your room. This indicates that you are sleeping.

How Does Actigraphy Track Sleep?

Usually, actigraphy permits the actigraph sensor or 3-axis accelerator in fitness trackers to record all movements made by you, whether they are big or small.

Sleep parameters are formed by experts and then programmed through a series of algorithms to interpret all movements detected by the fitness tracker based on the set parameters.

Actigraphy is used to record different sleep tests. These tests are used to evaluate depression, dementia, and circadian rhythm sleep disorders. It can also provide useful data about sleep in the laboratory and sleep in the natural environment.

However, it has been shown that it is not the first choice during important scientific research where the collation of data is required. This is because of its errors and inaccuracies.

How Accurate Are Sleep Trackers?

Fitness trackers depend largely on actigraphy to ascertain sleep quality. Actigraphy can record sleep percentage, the length of sleep before arousal and total time slept per night. 

However, it is not the best device to track the time of sleep and quality of sleep because its results are not always reliable. They are characterized by a wide range of inaccuracy. 

They might not be able to differentiate between sensitive sleep and regular sleep. Also, it requires its users to put them in their correct mode (sleep mode) when going to sleep and turning it off when they are awake. Sometimes, you may forget, and the sleep tracker records the wrong data.

For example, they might record that you are asleep when in the actual sense, you forgot to turn off the sleep mode.

LULUSILK Mulberry Silk Sleep Eye Mask & Blindfold Large with Elastic Strap/Headband, Soft Eye Cover for Women Men Deep Night Sleeping, Travel Nap with Fashion Stripe (Pink Stripe)

Buy this LULUSILK Mulberry Silk Sleep Eye Mask on Amazon

Types of Sleep Trackers

Most people believe that sleep trackers all come in the same form, smartwatch or bands. This is not so as they come in different forms. The types of devices you have determine the sleep component it will measure.

There are two types of sleep trackers, they are wearable sleep tracker and non-wearable sleep tracker.

Wearable Sleep Trackers

They are devices worn on any part of the body, usually as a band or watch around the wrist or worn as a pendant around the neck. Examples of wearable fitness trackers are jawbone, apple watch, and Fitbit.

Non-Wearable Sleep Trackers

These devices are not worn on any part of the body. They are basically thin strip, which lies above or underneath your mattress. They could also be a device that is kept on the nightstand table in your bedroom or an application on your phone. 

Below is a chart that shows a summary of different types of fitness trackers, parameters they measure and examples of these devices.

S/NoKind of Sleep TrackersParameters Examples of Devices

Wearable Sleep TrackersNoise, heart rate, body movement.Fitbit, Withings, Jawbone, Apple watch.

Mattress sleep trackersNoise, Heart rate, body movementWithings sleep tracking pad, Beddit, Tomorrow Sleeptracker monitor.

Smartphone applicationNoise, Body movementMotionX 24/7, Sleep Cycle Alarm Clock, AutoSleep.

Sleep Tracking HeadgearHeart rate, Body movementDeep Sleep Headband, Philips SmartSleep.

Nightstand Sleep TrackersMotion, Temperature, NoiseSleepScore Max Tracker, Resmed S+.

Your sleep tracker functions according to the technology used in its making. Basically, wearable sleep trackers need you to wear it before you sleep every night. Then it relies on the actigraphy sensor to monitor your sleep and sleeping patterns and if it has a heart rate sensor, it will measure heart rate.

While for a non-wearable sleep tracker, you may go straight to bed since you don’t have to wear it on any part of your body. For the mattress sleep trackers, the sensor inside the strip begins to work immediately it notices your body weight. 

For smartphone applications, instructions vary from one application to the other but basically you are asked to turn on the application and keep your phone on the bed beside you.

Buy this SleepScore Max Sleep Tracking Device on Amazon

How Smart Alarm Feature Works?

Most sleep trackers model has a ‘Smart Alarm’ feature, that wakes you through a vibration during the light stage of your sleep. Program a time frame for your wake up like 7:30 am and 8:00 am. The sleep tracker device will rouse you within the time frame when you are in a light sleep.

Like earlier discussed, these devices are said to be unreliable in their data collection and so might not be able to know if you are in a light sleep. This is so because they cannot measure brain waves.

However, they may give a good presumption. When we are sleeping, we go through all the phases of sleep about 4 to 5 times per night. Rapid eye movement sleep forms a longer part of each successive stage.

Sleep trackers can estimate when you will be in a light sleep phase from the time you sleep and uses the data from heart rate.

Importance Of A Sleep Tracker

Sleep trackers monitor your sleep patterns, as a result, they know when you are sleeping and the total time you were asleep. So, you will appreciate this device if you love to know you are being monitored to reach your fitness goal.

The ideal number of hours you should sleep every night is seven to eight hours. Sleep trackers help to monitor your sleep and ensure that you have enough sleep every night. If you have a model that has a microphone, use it to check if you snore when you are sleeping at night.

You can decide to take the information gotten from your sleep tracker seriously or not. But if you get overly stressed while you monitor your health closely, the sleep tracker is not a good choice for you.

You might become so preoccupied with monitoring your sleep pattern, a condition called orthorexia.


While it is not entirely reliable to use fitness trackers to track your sleep, it can be a guide to monitoring your sleep patterns and achieving your fitness goals. 

Fitness trackers that track sleep have an actigraph sensor that helps it to keep a record of the time you fall asleep and the time you wake up. It also monitors all other movements during sleep and is very good for people who suffer from sleep disorders.

If you have any questions, suggestion or comments, then drop them below. Let us continue the conversation.

Leave a Comment