[zmmmmm]

Well, that's why I say "being treated"

I'm not aware of many bluetooth headphones that blink an obvious light just because they are recording. You can get a pair of sunglassses with a microphone and record with it and it does nothing to alert anybody.

Whether it's actually legal or not, as you say, varies - but it's clear where device manufactures think the line lies in terms of what tech they implement.