Button-cams have been around for decades.

Idk, imagine if your friend was wearing a wire. Like he's a snitch for the cops. He comes over to hang out, and you're not breaking any laws, and he's actually not getting paid by anyone to record your conversation, but he's recording anyways.

Idk, that's creepy. Recording someone when they don't know of is creepy. Even if you say they have no expectation of privacy in public, they kinda do have expectations of privacy when the recording device is literally hidden. Like, if we have a conversation in public, it's still our private conversation.