A transponder apparatus having an identifier associated therewith includes a receiver for receiving an RF signal transmitted by an interrogator, a power source and a processing unit that is operatively coupled to the power source and is capable of being in an inactive, sleep state (low current draw)...http://www.google.com/patents/US7375637?utm_source=gb-gplus-sharePatent US7375637 - Methods and apparatus for reducing power consumption of an active transponder
