Charge 6 tracked heart rate without using it

[JLSomerset]

I went for a level walk two days ago, a very warm day. Because of the heat/sun I took off my Fitbit and put it in my bag. I wasn't that surprised that it recorded around 16,000 steps as it will have been sensing motion similarly to when it's on my wrist. However, I was VERY surprised that it recorded a heart rate for the whole walk, including two spikes into over 160bpm - said heart rate would probably have seen me collapsed by the roadside. Repeat... I WASN'T wearing the device... so how could it be recording a heart rate? Was it going bonkers in the heat? I had expected a blank space on the graph for the hours when it was in my bag (just as I usually get when I take it off)... instead I got a steady up-and-down reading and these super-high peaks? Any ideas why this could be happening?

Moderator Edit: Clarified subject

[LZeeW · Accepted solution]

Hello @JLSomerset and welcome to the Community.  Every Fitbit can create a false heart rate trace if the green LEDs don't turn off when you take it off your wrist.  The green light got reflected back to the sensor, creating this false trace.

[JLSomerset]

Really helpful answer - many thanks Laurie.