The present invention is remote control system including one or moree portable units and a base unit which employs identifiction codes for security. The operator preferably can select the identification code for the base unit, preferably via a process yielding a random number, with a provision for selection...http://www.google.com.hk/patents/US5148159?utm_source=gb-gplus-share專利 US5148159 - Remote control system with teach/learn setting of identification code
