Abstract: A security system consists of a central digital processor system, e.g., a general purpose computer, to which plural remote units are connected by a digital communications link, e.g., telephone. The remote units include plural alarm sensors such as intrusion and heat sensors. In a data base of the central processor system are stored segments of data associated uniquely with remote premises having the remote units. The processor system includes a terminal for delivering alarm message reports, such as to a law enforcement agency. Specifically, the remote units have interrogation circuitry for interrogating the sensors to determine if they have been tripped, logic circuitry for causing transmission to the central processor system via the communications link of a sensor alarm data message in digital format signifying the sensor address and its tripped status.