The B312RL has been designed to provide interfacing between a Series 300 detector and a 12V fire system or security system that require an external contact to activate an ancillary piece of equipment. The relay is controlled directly from the detector. Therefore, in an alarm condition both the detector and relay base will latch into alarm, and can only be reset by removing the supply voltage from the detector. The base can be used with 4 wire security systems that have a reset facility.