Abstract: A plurality of alarm conductors are coupled to a multiplexer which connects the conductors one at a time in sequence to the input of an alarm detector which detects alarm conditions on the conductors. A shift register having the same number of stages as the number of alarm conductors has its input coupled to the multiplexer output and its output coupled back to its input to form a recirculating serial memory. The shift register is clocked in synchronism with the multiplexer. The output of the shift register is selectively coupled through a switchable memory output control to the input of the alarm detector to recall a previous alarm condition on one or more of the alarm conductors. A second shift register having a number of stages equal to an integral multiple of the number of alarm conductors has its input coupled to the output of the alarm detector means. The second shift register is also clocked in synchronism with the multiplexer.

Abstract: Fire alarm and intrusion alarm conductors are wired from a plurality of dwellings to a nearby data transmitter circuit which is linked by a single pair of conductors to a remote data receiver circuit. The alarm conductors are sequentially scanned in the data transmitter circuit by a binary counter which sequentially enables or opens gates that are coupled to the alarm conductors. When an alarm condition is detected on one of the alarm conductors, the scanning counter is stopped and the counter number is converted from parallel form to serial form. The serial number is transmitted from the data transmitter circuit to the data receiver circuit. The least significant bit of the number signifies whether the alarm is a fire or an intrusion. The remaining bits signify the location. In the receiver circuit, the received data is converted back to parallel form and is printed out on a printer. The transmitted data includes a first bit which is always a binary 1 and a last bit which is always a binary zero.