Abstract: A multiple annunciation system for a building, including a master unit and a plurality of remote units connected to the master unit by electric power wiring extending throughout the building. Each remote unit generates a characteristic code signal, and transmits this signal to the master unit over the power wiring. The master unit is programmed with a series of reference values corresponding to the individual remote units in the building, and the incoming code signals from the remote units are compared and checked against the corresponding reference values. Absence of an incoming code signal, due to an interruption in transmission of a remote unit, produces an alerting signal identifying the particular remote unit which has ceased to transmit.