Abstract: The invention concerns circuit testing devices for connection to an existing electrical circuit to determine whether or not power is present across a pair of conductors. The devices are characterized by having a selector switch which may be placed in either a first position, wherein the device is so connected that an audible signal is emitted only when power is present across the conductors to which the device is connected, and a second position, wherein the audible signal is emitted only when power is not present. The device is disclosed in an embodiment which may be used with either AC or DC circuits, each at various voltage levels, and in a further embodiment wherein the audible alarm is actuated by a radio receiver which receives signals from a transmitter connected to the circuit being tested.

Abstract: A self-contained unit intended primarily for tracing the circuit connection between electrical outlets and a circuit-breaking connection thereof to an AC power source. The unit includes a housing containing batteries, a buzzer or other sound-producing means, an AC relay and a switch for selective placement in either of two positions. An electrical cord extends from the housing and terminates in a male plug for insertion in a receptacle of the circuit to be traced. By placing the switch in its first position the buzzer will sound when the AC power is supplied to the receptacle; placing the switch in its second position will cause the buzzer to sound when AC power, initially present, is removed from the receptacle. A second embodiment adds to the foregoing the capability of testing unpowered circuits for continuity between two conductors by incorporating an additional selectively positioned switch.