How do activity trackers know when I’m asleep? How they deduce REM sleep, deep sleep etc?
In: Technology
I believe they just measure your heart rate. It goes down significantly when you go to sleep
They do it by Actigraphy. Smart watches mostly come with extremely sensitive motion sensors, which keep a track of our movements in every direction and then translate those movements into sleep patterns. Still, calculation of REM sleep in particular is not very accurate as we have to do an EEG to record brain waves during REM sleep. They mostly indicate whether a person is asleep or awake.
Heart rate monitors combined with the accelerometer (sensor that tells if you’re moving) then put through an algorithm that includes normal sleep patterns. So, you would see the heart rate drop, light movement (non-REM sleep) for 90 minutes, followed by 10 minutes of no movement (REM sleep), then 90 minutes of light movement, 10 minutes of no movement. The algorithm can infer that the 10 minutes periods are REM, but it can’t confirm it. You would need some sort brain wave monitor to be absolutely sure you’re in REM.
Mainly the combination of no motion and heart rate variability. Everyone will have slightly different heart rates at sleep, the question is what is the difference between sitting very still and relaxed and being asleep. The answer is heart rate variability, and it isn’t an exact measure. For example, I have been awake watching TV and my Garmin thought I was asleep. Sleep studies do similar things but also listen for snoring and read your blood oxygen level. That is still essentially a guess as someone has to actually listen to you the recording to make sure you were actually asleep.
The tracker do it mainly with two sensors. Heart beat and accelerometer sensor.
– it detects sleep when you dont move for a long period of time plus Hearrate goes down. Some like fitbit even check if you are sleeping if by checking for twitching and small sudden movements like rolling over.
– it detect different sleep cycles by checking the change in heartrate. Between changes of stages, your heartrate will change ever so slightly.
– the watch does not do any calculations. It just records and sends data to your phone which then interprets it all the sensors and matches everything and decides yep you are sleeping let me label it.
More info:https://help.fitbit.com/articles/en_US/Help_article/2163#AutomaticDetection
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