How does Fitbit HR know when I fall asleep?

[Choreo]

I have only had mine 3 days and been looking at the sleep analysis.

It shows "Time to fall asleep" = 0 Min.? I lay in bed for usually 1-2 hours and read or watch TV before turning out the lights and trying to go to sleep so how would it know when I have decided to go to sleep and actually fell asleep?

It says "You went to be at 12:04 am", but I was actually in bed at 10pm, but did not try to go to sleep until about 12:04am... how does it know this??? I cannot figure out how it knows when that transition occurs? Why does it not think I "went to bed" at 10pm when I was in bed?

Also last night I woke up 5 distinct times that I remember and it recorded 2? The night before (as far as I know) it was right on.

I am just curious how it "knows" when these things are happening?

[SunsetRunner]

Magic..

Actually it assumes started to dream when wearing the tracker but laying still for at least a hour.. 

[LarryLakes]

Heart beat and dreams also its amazeing

[Choreo]

So, if you lay down, fall asleep, and then wake up 45 minutes later, it does not see that as "sleep"?

[awood08]

I've had it track small portions of sleep but nothing under an hour

[betpchem · Accepted solution]

@Choreo It goes by movement. Probably when you are lying in bed and reading, you are moving about. When you turn off the light and lie down, you are much more still. Similarly, if you woke up, but didn't move - just closed your eyes and went back to sleep - the Fitbit will not know you woke up.

[kalimm]

I always thought that it had more to do with your slower heart rate than with how still you are. I've got a couple of sleep logs that are 40 minutes and 52 minutes. 

[vlaura]

Hi!

I created a fix for this problem and posted it over here (click) under HR help forum. Hope this helps. 🙂

[CallieM]

Hey @Choreo did you see @betpchem's reply? 

She is correct in telling you that the movement of your tracker is mainly what constitutes "asleep time." As she mentioned, when you're reading in bed, you're likely still moving about, and not as still as you would be if you were sleeping. This movement while reading is how your tracker still knows you're awake, and when this movement stops as you fall asleep, this is when sleep recording starts.

I hope this clears things up, and please let me know if I can answer any further questions!

[Happy2B]

Found this on the Fitbit website. "Fitbit estimates your sleep stages using a combination of your movement and heart-rate patterns. When you haven't moved for about an hour, your tracker or watch assumes that you're asleep. Additional data—such as the length of time your movements are indicative of sleep behavior (such as rolling over, etc.)"

[johnlsummey04]

In fact it presumes started to dream when using the tracker yet laying still for a minimum of an hour.