How does a Samsung Galaxy watch track sleep?

In this brief guide, we are going to answer the question “How does a Samsung Galaxy watch track sleep” and provide you with more tips on how health activity is measured with smartwatches.

How does a Samsung Galaxy watch track sleep?

The Samsung watch tracks sleep by measuring the Heart Rate Variability (HRV) and wrist movements made by the wearer of the smartwatch.

Galaxy Watch Active2 and Watch3 comes with the inbuilt ability to track your sleep when you wear the watch to bed. 

To start the tracking process Samsung states to “Go to your apps tray and open Samsung Healthtap on Sleep and there you can see all your sleep tracking information. When you’re ready for bed, tap Start to begin the tracking to see if you’re getting a restful night’s sleep.”

How do smart watches track health activity?

The most basic way a smartwatch tracks health activity is by measuring heart rate. The heart rate follows a specific pattern or cycle in the sleep state which forms the basis for sleep tracking and is discussed in detail below.

What is the best way to measure heart rate for sleep activity?

The best way to measure cardiac cycle activities would be via electrocardiography method, however it requires that electrodes be mounted directly on the chest, which is definitely not a feasible way for everyday use. 

How is heart rate measured with smartwatches?

Smartwatches come with built in sensors that measure heart rate. The method deployed in smartphones to measure the heart rate is via the photoelectric pulse wave method. Photoelectric comes from “photo”-Greek origin ‘light’ and electric meaning the output is in electrical form. In essence light sensors translate the measured activity and give an electrical output, which is stored by the smartwatch.

There are two methods used in this optical sensor approach as explained below. 

Transmission type method

The first is a transmission-type pulse measuring sensor which many smartphones come with the feature of or an easily downloadable app that works on most smartphones. 

This method relies on emitting red or infrared light onto the body where the skin is thin and light can easily penetrate, generally the fingertip is good for such measure. 

The optical sensor senses the disruption in transmission of light as the heart rate increases and decreases blood flow in the capillaries below the skin. 

Reflection type method

The other method also comes under the same category but is a bit advanced as it depends on the reflection of light from the incident. 

Initially similar to the transmission type, infrared light is emitted towards the body. A photodiode or phototransistor then measures the amount of reflected light. 

Blood carries oxygen to all parts of the body.The hemoglobin present in the oxygenated blood has characteristics of absorbing incident light. As blood flows through the capillaries, the blood flow rate can be determined by the amount of light absorbed and reflected. 

Between heartbeat contractions the amount of blood volume absorbing and reflecting the light would change, which can be measured in pulsating waves which gives readings of the heart rate.

How do smartwatch heart rate measurements help track sleep?

Smartwatches not only measure heart rate but as the word says “smart”, the heart rate data is extrapolated to represent variations in sleep cycles and differentiating rest and exercise heart rates.

 Along with that wrist movements are also tracked that combined with the heart rate readings give a more accurate take on the sleep tracking. 

Much like the difference between speed and acceleration, the Heart Rate Variability (HRV) is a measure of how the heart rate changes between different activity levels and this helps differentiate the stages of sleep. Namely there are 4 stages of sleep:

What are the 4 Stages of sleep?

The lightest sleep: 

This is termed as the awake sleep betwixt state, where a person is consciously present as well as in a sleepy state. This is a short period of 5 to 10 mins after which the actual sleep starts.

The light sleep: 

This is where the heart rate starts to slow down and body temperature starts to drop a bit to adjust to the slower heart rate. 

This phase lasts about 15-20 mins and can extend to an hour in a not-so-good sleep.

The deep sleep: 

This is the state of sleep where if awoken from this stage a person feels disoriented, this stage is short and this is when the body is in its repair mode or maintenance. This lasts about 20-40 mins.

The REM sleep: 

This is called the Rapid Eye Movement stage of sleep. At this point, the heart rate and brain activity peaks overall and this results in the person seeing dreams. This is a short period of 10 – 15 minutes but as the cycles of sleep progresses, the REM sleep gets longer and can reach about 90 minutes.

The 4 stages of sleep repeat themselves in the same order till the time a person wakes up. The smartwatch measures the changes in heart rate and tracks the data so it can recognize the REM sleep and can inform the wearer about how the sleep progressed the previous night.

How is the Samsung Galaxy watch useful in tracking sleep?

The Samsung Galaxy Smartwatch can be very useful for people suffering from sleep disorders to track and communicate their problems to their respective doctors. 

As for the busy man it can help to decide which times are best for their sleep for example, does the 11 pm to 6 am slot suit better in sleep productivity or the 12 pm to 6 am slot with an hour’s nap between the day give a more fulfilling sleep schedule. 

Either way, it can benefit people who find it hard to find the time, energy, or resources to balance their work-sleep life.


In this brief guide, we answered the question “How does a Samsung Galaxy watch track sleep” and provided you with more tips on how health activity is measured with smart watches.

If you have any questions or comments please let us know.


HRVHeart Rate Variability. It is a measure of the variability of heart rate between two consecutive heartbeats.
HemoglobinProtein present in the Red Blood Cell of human body that carries oxygen to the body
PhotoelectricPhoto derived from “photo”-Greek origin ‘light’ and electric meaning the output is in electrical form.
REMRapid Eye Movement. The state of sleep characterized by random rapid movement of the eyes, accompanied by low muscle tone throughout the body, and the state of sleep where dreams occur.