There are states (the others not mentioned) that have what’s known as a “single consent” law, where only one party has to consent to the audio recording. However, this would require the person who’s using the camera to actually be present at the time of the recording, which is basically never the case with a nanny cam. This tends to apply to “body worn” cameras – sunglasses, pens, buttons, etc.

And then in the states mentioned, they require all parties to consent to an audio recording. However, it is important to note that even in a single consent state, this doesn’t allow for use of audio in nanny cameras, since these devices are used to record while one is away (and therefore not party to the recording and so is unable to consent to audio recording).