Burn mark after wearing Pinetime?

[Avamander]

I have been wearing my Pinetime basically nonstop since I got it. I took it off just now and there is a burn mark on my arm where I was wearing it. Has anyone else experienced this, and should I be worried?

I'm confident this is not any form of allergic reaction to the materials of the device as this burn is exclusively under the sensors on the backside of the pinetime. I think the sensors somehow burnt me, but the device itself never got hot to the touch.

Just physical friction? The hardware as such is simply not capable of generating anything dangerous.