A system to enable individual locator devices or badges developed for location of people or objects to (1) determine whether their identification transmissions are received by sensor stations and to (2) take appropriate actions when the transmissions are not received. Each badge in the system can transmit...http://www.google.fr/patents/US5471404?utm_source=gb-gplus-shareBrevet US5471404 - Occlusion detection system for locator devices
