Home / General / How Do Fitness Trackers Measure Sleep: The Science Behind It

How Do Fitness Trackers Measure SleepFitness trackers definitely have come a long way from where they first began. Initially, these bands were only capable of determining the number of steps you take every day. Then they got more hi-tech and began to display the number of calories you burnt in a single day. They can even see your progress in different sports. Now, these trackers can display your pulse per minute and also give you a detailed analysis of your sleep pattern. Such makes a lot of people curious about how do fitness trackers measure sleep.

As similar to any wearable technology, these fitness trackers have science behind them. They are usually a miniature version of old procedures or equipment, but the principle is the same or almost the same. Hence, if we want to understand how they work, we must also have a deeper knowledge of what they measure, which is sleep.

Sleeping: A Brief Science

Sleep is divided into two phases. The first one being NREM, that is Non-Rapid Eye Movement. The second phase called REM or Rapid Eye Movement follows this. Each of these two can be further divided into three different stages of NREM sleep, and then followed by one REM phase which takes you from the minute you fall asleep to the moment right before you wake up. In each of these sleep phases, there are different levels of brain activity. These include eye movement, muscle tension, breathing and blood pressure.

People who research sleep more scientifically choose a technique called the polysomnography which is only performed in laboratory conditions as it requires multiple wires being attached to the subject to study the multiple channels of the data. This is considered to be the gold standard for measuring sleep as it is guaranteed to give you 100% accurate results of your sleeping habits.

How Do Fitness Trackers Measure Sleep: A Closer Look

One of the most popular fitness trackers on the market right now is the Fitbit. This tracker uses accelerometers in order to track movement which includes the speed and the direction of your motion. This is the way it tracks all of your activity throughout your day and can also tell you when exactly you fell asleep.

Most trackers these days have a three-axis accelerometer that tracks every single movement. Some even come with a gyroscope to measure rotation and orientation. These are capable of collecting all the data, that is all the activity, calories and sleep analysis for the day. These are not 100% accurate, and there is guesswork on the part of the tracker in order to fill those parts that have no data.

So, when you sleep with your fitness tracker, it will carefully monitor all of your movements. While you are asleep, you are likely to have minimum to no movement at all. When the tracker does not detect any movement for a specified period of time, let us take one hour, in this case, it will assume you have fallen asleep. This technique is called actigraphy, and each tracker’s manufacturer will have a proprietary algorithm in order to interpret the data.


When scientists study sleep, they used a device called an “actigraph”, which is similar to a fitness tracker. This device is typically worn on the wrist and tracks all the movements while you sleep. The software will then translate all the movements into different periods of wake and sleep.

People who suffer from sleep disorders or those who have disruptions during their sleep will benefit a lot from actigraphy as it is a very convenient method to track their sleeping patterns by a clinic without having the need to sleep in a lab.

The Algorithm

As mentioned earlier, no fitness tracker will give you 100% accurate results for any activity, including your sleep. Even if you use two different fitness trackers, there will be a difference in the results between the two. This is because the sensors that are inside the trackers are not perfect to measure exactly every single activity. Each tracker uses slightly different algorithms in order to translate all of the raw data into readable and actual statistics.

What are Some of the Benefits of Sleeping with a Fitness Tracker?

Although some sleep experts are still skeptical about these fitness bands’ accuracy and it may not necessarily be 100% accurate, the results are quite close to it. Likewise, wearing one offers a lot of benefits.

  • Wearing a fitness tracker provides you with helpful insight into your sleep which will enable you to have a better understanding of it, and also stop you from constantly hitting the snooze button on your alarm.
  • Fitness trackers give a comprehensive data of when exactly you fell asleep and woke up as well as how long you have been in a deep sleep.
  • Some fitness trackers can also give you data about the disturbances and even awakenings during your sleep. Most analysis will show your data in the form of a graph.
  • While only a polysomnography testing in a sleep lab can diagnose any kind of sleeping disorder, knowing the results of your sleep analysis will help you determine if there is an issue with regards to your sleep and give you a heads up if you should visit a physician about it.
  • Ultimately, the primary benefit of wearing a fitness tracker while you sleep is in helping you analyze your sleep better and thus be able to help improve your sleeping habits.


We are certain that this article has given you enough on how do fitness trackers measure sleep. In a nutshell, the accelerometer and the actigraph are what is majorly responsible for measuring your sleep. These give you a clearer idea of your sleeping pattern. However, only a polysomnography testing will be able to exactly measure your sleeping pattern and be able to diagnose any sleep-related disorders.

Nonetheless, for what it’s worth, a fitness tracker is a fantastic device that will help you measure your sleep and is useful especially when you want to view your long-term sleeping patterns and have a better understanding about it.