A motion activated alarm that says something like "your presence has been detected, and the your movements are being recorded". Then it either changes to a different message, or there are Two separate alarms, the other said something about unauthorized activity, and using your ID card to prevent a police response. Its just waffle, just an audio to spook people out. It worked on me! I bugged out, and went back when I was feeling braver!
That'll be a PIR then