A system and process for determining the location of persons and objects using transmitters (TXs) that transmit location messages to at least one receiver connected to a computer, in a network of computers. The TXs are small, battery-powered, radio frequency transmitters carried by the person or object...http://www.google.de/patents/US6720922?utm_source=gb-gplus-sharePatent US6720922 - Radio-frequency badge for location measurement
