When You Install a Surveillance Camera

I have read that cats always keep up with their human's whereabouts in the house even they can't see us. When we are gone, they are very aware of it. So when the householder installs a surveillance camera with two-way audio, and then talks to the cat, you can imagine their shock. What is this witchcraft? It's mama's voice, but mama left hours ago! They all recognize the voice, but their reactions run the gamut from delight to panic.