Abstract: An access control system for controlling and monitoring access to selected restricted areas and "alarm" conditions at such areas. The system comprises a central controller unit which repeatedly polls a number of remotely located reader terminals and alarm monitors. The reader terminals are adapted to receive and "read" magnetically encoded card keys issued to personnel and to sense "alarm" conditions at such areas. When a card key which has a proper facility code on it, is inserted into a card activated lock, a card reader at a reader terminal determines whether the card key is magnetically encoded so as to meet all entrance criteria stored in a memory of the central controller. If the card is properly encoded, access is granted to the cardholder at that location.