Different digital radio transceiver front panel escutcheon plate modules are provided for different optional transceiver configurations. A security circuit is provided in each module in addition to user controls and associated circuitry. The security circuit is connected to communicate serial data signals...http://www.google.com.au/patents/US4941174?utm_source=gb-gplus-sharePatent US4941174 - Digital radio with security system for selectively enabling software controlled options
