Before buying a security camera, ask yourself:
Laws vary from state to state regarding the audio element of a surveillance camera, but on a federal level, the requirement is that one person needs to be aware of the recording. Because this is the federal law, it makes it impossible for any state to allow zero people being aware.
So what this means is that it's illegal to audio record in the form of eavesdropping. It's prohibited, for instance, to secretly record a conversation that two people, without them being aware, are having across the room at a coffee house that you're all in.
However, that federal rule that one person needs to be aware of the recording means that you can get away with "secretly" recording those two people-as long as you're part of their conversation, sitting right with them. So if those two people learn you recorded them, they can gripe all they want, but you're protected by federal law since you sat and talked with them.
The law for audio recording isn't the same as for visual, in which the latter is allowable for publically seen environments. This is where "Dual Consent" comes into play for ANY audio recording. Some states require both parties need to consent to audio recording in order for the recording to commence.
These rules apply to phone conversations as well as cameras, which is why you often get an alert that your customer service call "may be recorded for training purposes."