Cat motion detector that can tell the difference from humans I'm trying to build a cat motion detector but, to avoid getting false alarms when a person walks by, I was thinking of using RFID. i.e. the cat has a collar and the detector senses the collar when they get within a couple of feet and makes a noise.

The problem there seems to be with RFID is that the range is so short - e.g. 4".

Anyone have a better solution?
Place an additional motion sensor such that it can only detect motion from things significantly taller than cats, and use that as an inhibitor/classifier of the cat motion signal.