Abstract: The detector assembly is connectable to a power line which includes a switch which, when operated, causes power transitions at a power terminal for the detector assembly. The detector assembly includes a code responsive controller which operates in response to a plurality of power transitions occurring within a predetermined time period to deactivate a detector alarm for a determined delay period. The code responsive controller may also operate in response to different numbers of sensed power transitions to control the activation and deactivation of a light forming part of the detector assembly. A code transmitter responsive to the activation and deactivation of the detector alarm transmits an activation code and subsequently a deactivation code over the power line to activate and deactivate other detector assemblies, and a code receiver receives activation and deactivation codes from the power line and controls the activation and deactivation of the detector alarm in accordance therewith.