Abstract: A building security system for coupling to a building telephone line which includes a building subscriber telephone line connected to a subscriber telephone set on one end and to a central office line at the other end. The central office line leads to a central office exchange. The building security system controls communication between a central office exchange caller, a subscriber and a visitor at an intercom station in order to allow subscriber control of visitor entry and for allowing entry without subscriber control to authorized personnel. The system includes a micro-controller, a non-volatile memory coupled to micro-controller which is programmable for storing system parameters including security entry codes and a building door latch of an entrance door which is coupled to the micro-controller. The latch is operative in response to a control signal from the micro-controller to unlock the associated entrance door.