Abstract: An alarm system includes: (1) a central station having power generating means and alarm registering means, and (2) a plurality of alarm-producing systems in locations remote from the central system, each electrically connected to the central station through a single pair of conductors, and each including circuitry for producing up to eight separate alarm conditions as the power generating means alternately impresses a first predetermined DC voltage on each pair of conductors simultaneously, then interrupts voltage to all conductors simultaneously, impresses a second predetermined DC voltage only on the first of each pair of conductors simultaneously, and again interrupts voltage to all conductors simultaneously.