Abstract: An electrical unit, such as a fire or gas detector, carries a three conductor plug for receipt of energy, AC hot, and neutral, as well as for coupling to a bidirectional signaling line. A multiple conductor adapter makes it possible to couple the plug to a plurality of incompatible, previously installed sockets. The adapter can be fully contained in a single housing. Alternately, it can include a housing for some of the conductors with the remainder carried on a cable which extends from the housing.