I was going to say that this is the only surveillance that I would be OK with, considering the users are not on public property. However, I hadn't considered that calling the police on anyone in the US (especially for carrying a firearm) does not carry the same consequences as elsewhere...

Yeah, most (but perhaps not a super majority of) people in the US know calling the cops has a large chance of excalating a situation and making it deadly, especially if a gun is mentioned in any context.