An electronic access control system comprising a lock cylinder and one or more user keys for use in operating the lock. Housed within the lock cylinder is a microprocessor and a memory. Each user key has an ID chip in which is embedded (at the time of manufacture) a unique ID number drawn from a pool...http://www.google.es/patents/US20050179544?utm_source=gb-gplus-sharePatente US20050179544 - Security system
