How does Garmin measure REM sleep?

In this guide, we will talk about how Garmin measures REM sleep, what is Advanced Sleep Monitoring, what type of information is recorded with Advanced Sleep Monitoring, why is REM sleep important and what Garmin Sleep reveals. As we will see, getting a good night’s sleep is extremely important and contributes to our overall health since many processes happen while we are asleep even if we are not able to notice them. 

How does Garmin measure REM sleep?

You may wonder how Garmin measures REM sleep, and here we have the answer. Garmin, in addition to using the accelerometer for sleep tracking, also uses heart rate variability data from the optical HR sensor to provide REM sleep tracking with this update. However, it is important to make sure your device’s heart rate monitor is on, and the device fits comfortably, not too tight or too loose. 

Scientists agree that having a good night’s sleep is very important, and you may even notice that something is different when you don’t. For instance, think about a night or a few nights when you haven’t had enough sleep. How did you feel the following day? I know I would feel very moody, cranky and tired. 

However, how important is REM sleep? REM stands for rapid eye movement and it is also known as the dreaming stage. Usually, REM sleep starts 90 minutes after you have fallen asleep and the first period of REM typically lasts 10 minutes. During this stage, your heart rate and breathing quicken. 

You may have recalled some intense, strange or nice dreams the following morning. Well, this is because of REM sleep since our brains become more active. REM is considered very important because it stimulates areas of the brain that helps us consolidate learning, memories and is also associated with the increased production of proteins. 

Advanced Sleep Monitoring

This feature is included within the newer Garmin models and trackers include an optical heart rate sensor for sleep tracking. Advanced Sleep Monitoring allows users to track and record their sleep statistics on the Garmin Connect App after wearing the device while sleeping. Moreover, some Garmin devices also include Pulse Ox that measures oxygen saturation and respiration metrics while sleeping, which is a plus.

Pulse Oximetry is a non-invasive method that measures the level of oxygen in your bloodstream and the respiration feature displays how many breaths you take in a minute. 

What information is recorded with ASM?

The information recorded with ASM are sleep cycles. Garmin is introducing sleep cycles that will provide information related to light sleep, deep sleep and REM sleep. 

During light sleep, eye movements and muscle activity begin to slow down as your body is preparing to go into a deep sleep. During this next stage, deep sleep, eye and muscle movements will stop completely and your heart rate and breathing pattern slow down. This stage is also referred to as restoration mode, where the body recovers, builds bone and muscle and boosts your immune system.

During the Rapid Eye Movement stage or REM is where you dream and brain activity is almost as active as when you are awake. REM is very important to form and consolidate memories and learning.

However, considering that Garmin Advanced Sleep doesn’t track naps, for me it is a great inconvenience because I do like to nap from time to time. There is a lot of research available showing the benefits of napping but the app will only take into consideration the length of sleep.  

Heart Rate Variability (HRV)

The optical heart rate sensor on the device will measure Heart Rate Variability which is the time measured between each heartbeat. Combined with the accelerometer, it allows Garmin to determine when you have fallen asleep when you’re awake and the sleep cycle you are in.

Some of the requirements to get ASM to include having a watch that is compatible with AMS, having the Garmin Connect App updated, the device must be worn at least 2 hours before going to bed and make sure the optical heart rate monitor is enabled. 

As indicated on, “Your ‘sleep clock’ is triggered to start when you get into bed and your heart rate drops to the levels the watch knows you sleep at. Based on your HRV this becomes more accurate the longer you wear the watch”. Unlike measuring your normal heart rate, which is the average number of heartbeats per minute, HRV focuses on small fluctuations of your heart. 

However, those fluctuations can be affected by many things such as age, body position, body weight, time of the day, stress, etc.

What Garmin Sleep reveals

After a good night’s sleep or in some cases a short (and not so good) night’s sleep, you can see the breakdown of the time you have spent in the different sleep stages and also the duration of any periods when you were awake.  However, the sleep stats will not be displayed on the watch itself but the Garmin Connect app or web tools.

Moreover, the app allows you to add a widget to get your most recent sleep time displayed on your ‘My Day’ screen. Also, you can get the breakdown by hitting ‘More’ and then tap into your health stats. If you see the timeline presented and you spot an error, you can manually edit the information in the Garmin Connect app and the web tools. 

But what about Pulse Ox? Well, since this measure will be recorded as you are sleeping, you will see a movement line showing the level of oxygen in your blood, also known as SpO2. The normal range is between 94 to 100% range. If you get a score particularly below 90% it may be a sign of health issues (i.e. sleep apnea). 

Why is this blog about How does Garmin measure REM sleep important?

As discussed on how Garmin measures REM sleep, it uses a combination of certain sensors such as the accelerometer and the Heart Rate optical sensor to track sleep cycles. However, remember that it is important to make sure your device’s heart rate monitor is on, and the device fits comfortably, not too tight or too loose to get the best readings.

Moreover, we have talked about how REM sleep is very important because it stimulates areas of the brain that helps us consolidate learning, memories and is also associated with the increased production of proteins. However, Garmin tracks other sleep cycle stages that we go through during the night that are also very important and contribute to our overall health. 

Please feel free to leave any comments or thoughts about the content of this article!

Frequently Asked Questions (FAQs) about How does Garmin measure REM sleep

How accurate is Garmin REM sleep?

Garmin indicates through their studies, “The matrix shows that the classifier predicts deep, light, and REM sleep stages at roughly the same 69% accuracy rate. Wake is slightly more accurate at 73%. The most common misclassifications are classifying true deep sleep as light sleep and classifying true REM sleep as light sleep”.

Why does my Garmin not show REM sleep?

If your Garmin is not showing REM sleep there is a possibility that it doesn’t have the technology to track heart rate variability accurately or the settings aren’t configured to measure sleep. For instance, the optical heart rate sensor must be enabled for it to track sleep stages such as REM.  

How do you measure REM sleep?

This is usually done at a sleep lab or centre. Scientists attach electrodes to your head to take three types of measuREMents while you sleep. The first measuREMent is the electrical activity of your brain, measured by a method called electroencephalography or EEG. The second measurement is muscle activity measured using electromyography and the third is eye movement, measured using electro-oculography.

Is Garmin or Fitbit better?

Garmin is better in terms of offering a greater emphasis on VO2 max and heart rate zones, which makes it the preferred choice for athletes. However, if you are looking for a lifestyle tracker then, Fitbit seems to be a very highly effective choice.

How does my watch know I’m in REM sleep?

Your watch knows you are in REM sleep using a process called actigraphy. Your tracker translates the movement you make into sleep patterns. Brainwaves, eye movements, and breathing are also required to determine when you are in deep sleep and when you are going through a light sleep stage.


What is Advanced Sleep Monitoring in Garmin Connect?