> If someone is in your home they're on your property, and generally you can record whatever you want in a single party state.

That’s simply not true. They’re called “one-party states” because there has to be one party in the conversation who knows about the recording. Some states are one-party, some are two-party, but there is no such thing as a zero-party state. It is always illegal to record a conversation between two people if both are unaware of the device and believe their conversation is private. The fact that they are in your home, your car (without you), or in your business is irrelevant.

You’re confusing laws that apply to video with laws that apply to audio. You can of course record images on a security camera in your home or business (except, as you said, in restrooms, dressing rooms, etc.) Audio is different.

Sources on this are easy to Google for. Here’s one in pretty straightforward language from a defense attorney’s website: https://www.criminaldefenselawyer.com/resources/criminal-def...

Interesting. Since the main test is "a reasonable expectation of privacy", I'm guessing that the majority of the time recording is still fine. If there's clearly visible cameras it could be assumed you're being recorded, at least on video, so you don't really have an expectation of privacy.

I guess the main problem would be if you hid the recording device

That’s an extremely high bar to clear. If two people are screaming at each other on a street corner with a crowd of onlookers it’s surely fine to record them. But if those same two people are quietly speaking to each other while you stand nearby with a microphone running, you’re violating the Wiretap Act. Same for recording the patrons behind you at a restaurant, the guy on a phone call on the bus, etc.

There are surprising edge cases to this. People have been found in violation of the Wiretap Act for putting microphones on their walls to collect proof that their neighbors are screaming too often. A loud argument in an apartment still has an expectation of privacy even if you can make out the words with your ear to the wall.