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How Does Fitbit Track Sleep? Here’s the Lowdown!

Today, a large number of devices are designed to help you track your sleep. This is, of course, fitness trackers for the most part including a few fitness trackers for children. 

Who would have thought that a type of wrist wear can keep you updated on your sleep patterns, right? No manufacturer, however, can do it as well as Fitbit. But how do they do it, you ask? In this article, we will look at the basic principles of how Fitbit tracks sleep.

So How Fitness Trackers Tracks Your Sleep?

Modern fitness trackers can keep track of which phase of sleep you are in at one time or another. To do this, they study your movements and measure the pulse. Of course, the tracker has to be in contact with your wrist. 

It works something like this… as an example, we configure the Fitbit tracker algorithms:

1. If the fitness tracker notices that you are immobile for an hour, then you are asleep and starts tracking your sleep.

2. If at the same time your heartbeat is slower than before, the tracker determines that you are in a phase of slow sleep. Depending on how much slower it beats, the device understands if the sleep is light or deep.

3. If you start to periodically move (turn over) and the heart rate is accelerated, the tracker understands that you have transitioned into REM sleep.

4. If you begin to actively move and move to a vertical position, the tracker determines that you are awake. 

5. After you wake up, Fitbit renders the statistics for your night’s sleep. 

How is this information useful for the average user?

Using the data that Fitbit has gathered, you can configure your sleep mode. Sleep and rest modes are something that will make you feel much better and more productive.

For example, Fitbit does it like this: it gathers your sleep statistics over a period of five days, the application sums up the average and gives you how many hours you should spend in a dream to go through all the necessary phases and rest.

You can also set your own sleep time when you think you’ve slept perfectly. Or you can compare your average sleep time with the norms for people of your gender and age and try to achieve that number.

After this, the application will monitor whether you sleep enough every day. For an adult, the rate of a good night’ sleep ranges from 7 to 9 hours. But each person is different, so the fitness tracker allows you to determine the exact time frame specifically for your body.

Types of Sleep

Types of Sleep

In order to track sleep quality, Fitbit works with the National Sleep Foundation to better understand each phase of sleep and based on this data is able to make individual recommendations for you.

Here is what Fitbit says:

Light sleep

The first stage of sleep is intermittent, shallow sleep, which does not allow the brain and body to rest. In general, it does not last long and is preparatory for the transition to the next phase. At this stage, you can still hear the surrounding sounds, react to light stimuli, feel some awareness and understand your whereabouts. 

The second stage is just a light dream, where you sleep, but you can easily wake up from any noise. Nevertheless, this stage is very important, because in it a healthy person spends more than half of his/her sleep. 

The body in these hours processes memories and emotions, the metabolism is engaged in self-regulation. We can say that light sleep is the stage of maintenance of the body itself. Breathing and heart rate usually become slightly lower than just at rest.

Deep dream

It consists of two more stages, where at the third stage you become less responsive to external stimuli, breathing slows down, and muscles relax, the pulse also decreases and becomes stable. Deep sleep is very important for the body, where in the next stage the muscles rest. The body is optimally prepared for self-healing. During this phase, the body begins to secrete growth hormone, which promotes cell regeneration. The immune system is strengthening and you don’t dream in most cases. 


You can say that deep sleep is for the body and REM is for the brain. During periods of sleep, the brain is very active and the body remains at peace. You are literally paralyzed while the brain is trying to the full extent. In this phase we see dreams and the eyeballs begin to move quickly in different directions (hence the name). Heart rate increases, breathing becomes irregular, which indicates emotional activity.

The REM phase is very important for emotions and memory. Also, the peak of protein synthesis at the cellular level, which ensures the proper functioning of many processes in the body is considered part of the REM phase.

Why do we need to know all this?

The body does not survive every stage of sleep once a day and does not spend an equal amount of time during each phase. All phases pass cyclically several times per night, where each cycle lasts an average of 1.5 hours.

A typical night looks like this:

Cycle 1: During light sleep, you plunge into the first stage and almost immediately go to the second. Then comes the phase of a deep sleep, where you stay for a while, followed by 10 minutes at REM.

Cycle 2: Light sleep lasts a little longer than in the first cycle, deep sleep is still quite long (but less than before), REM lasts a little longer.

Cycle 3: Light sleep lasts even longer, deep – less, REM – again, rather long.

By the time the night has is half over, you will experience three full cycles. Then the following happens: the cycles break down and deep sleep begins and the body alternates light sleep and REM. On average, the phase of light sleep takes about 50 percent of the night, where fluctuations do not affect on your well-being on waking up.

Deep sleep takes from 10 to 25 percent of all sleep, depending on your age. We have no way to determine its duration, meaning that we cannot make the body rest and recover. It will take care of itself and as soon as it feels that everything is enough, it will cease to enter this phase. During deep sleep, the body is most difficult to wake up, as it is trying to deal with this phase as soon as possible and switch to light sleep and REM.

A lack of deep sleep affects your well-being. You wake up still not rested. The duration of deep sleep interferes with age, illness and other sleep disorders. For example, a runny nose or an uncomfortable posture simply will not let you rest at night. A changeable work schedule also affects deep sleep, with the result that the body is less willing to plunge into a deep sleep during the day.

REM makes up about 20-25 percent of a night’s sleep and mostly occurs in the second half of the night. If you reduce the time for a night’s sleep, you minus this phase from it. Lack of REM makes you less concentrated, focused and can lead to memory problems. This is why it is important to get enough rest before any mental activity.

REM is adversely affected by many medications. For example, antidepressants can reduce REM by half. The too-long phase of this dream contrarily is also not beneficial because the brain becomes too active and this overstrain may leave you in a grumpy mood when you wake up. Furthermore, it also increases anxiety levels and aggravates depression.


Of course, all the given data is relevant for the average person, especially the numbers. To get more or less accurate parameters, analyze the data of other users of your gender, age and with the same level of activity through the fitness tracker application. Compare your performance with the average and use it as a benchmark to regulate the duration of your healthy sleep.

We are all different and our needs for rest vary. If you only need 6 hours rest, you do not take drugs that affect sleep, wake up refreshed, wake up full of body and mind energy, then note down your sleep schedule as a reference. We cannot influence the phases and phases directly, but we can shorten or increase the length of the night. That is what the sleep monitoring function in gadgets helps us do. 

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