US Patent 7800497 Wireless detection system

A system is disclosed including a transponder and a shield. The transponder may be a radio frequency identification (RFID) transponder and sends a signal to a reader. The shield selectively prevents the transponder from sending the signal. The transponder and the shield are selectively movable relative to each other to permit transmission of the signal from the transponder. A movement of the transponder and the shield relative to each other is indicated by the presence of the signal. Thus, when a signal is present, due to a change or increase of the movement of the shield relative to the transponder, the reader receives an indication of a disturbance or an intrusion.