IAALBNYL it’s not theft because they’ve been abandoned and are in the new owner’s possession. If the prior owner can’t be reached and the security company which claims to own them won’t take them, they’re probably fair game.
I do not see any way in which this property could still be considered the previous owners. Let's say the camera was in the bathroom pointed directly at the shower. You just have to suck it up forever, knowing that someone could be watching? In fact, I could imagine it being a criminal charge for trying to capture people in the nude. What if someone has a child who bathes there? Now they were trying to create CP.
Even if that were the law, you could disconnect the cameras or cover the lens.
What if it has microphones which are not so obviously obscured? I do not see why it should depend upon my technical acumen to non-destructively disable a surveillance device within my private space.
It’s property law 101 that possession and ownership are not the same thing.