Tags capable of wirelessly transmitting unique codes when energized by radio frequency (RF) energy are used to identify a variety of different locations and objects. A portable battery-powered unit having digital storage capabilities is designed to be transported to the general location of the tagged...http://www.google.com.hk/patents/US4688026?utm_source=gb-gplus-share專利 US4688026 - Method of collecting and using data associated with tagged objects
