A mobile controller unit has a radio positioning system and a two-way communication system and a rover unit also has a radio positioning system and a two-way radio communication system. The controller unit can query the rover unit to send its location data so that the rover unit can be located and if...http://www.google.co.uk/patents/US20030195008?utm_source=gb-gplus-sharePatent US20030195008 - Locating system and method
