Abstract: A system for testing a remotely located sensing unit includes a photosensor located within the sensing unit. A control beam of incident electromagnetic energy can be provided from a remotely located portable source such as a flashlight. Directing the beam of radiant energy from the flashlight against the sensor in the unit causes the unit to initiate a test sequence. The unit can be equipped with a photo-detector to terminate an alarm generated in response to a sensed condition. The unit can include a sonic detector. Control circuitry in the unit can decode a sensed encoded incident beam to minimize false tests or to provide multiple remotely initiated functions.