IsItBullshit: Your phone is never truly "off" and governments/hackers can still listen to/track you. (Any tech dudes)

So I have no idea about this shit, and this always sounds very conspiracy to me, but I've heard a surprising amount of people saying that even if you're phone is switched off, your microphone can still be hacked, accessed, "they're always listening", etc etc.

I can see why it would be useful for security purposes to be able to do this, but it also sounds very Jason Bourne paranoia to me?