A device for generating an alarm signal in the event of an abnormality in the environment of a detector includes a pair of signal/power supply lines, a number of detectors for detecting an abnormality, e.g., fire, gas leakage, or burglary, and an alarm receiver including a signal processing circuit for receiving a signal from a detector indicating the presence of an abnormality. The signal process circuit includes a signal storage circuit, and a converting circuit for changing one or a combination of at least two of a polarity, voltage, current, or impedance of a power source if the abnormality persists for a predetermined time. The change in the power source parameter is supplied via the supply lines to a signal holding circuit in the vicinity of the detector. The signal holding circuit is responsive to the changed parameter and changes state, thus providing an indication at the detector that the abnormality has persisted for the predetermined time.