Abstract: An apparatus to indicate a state where a communication device connected to a communication wire and a power line is protected from a surge current. A toroidal coil picks up a rapid increase of current caused by a rapid increase of voltage that occurs in the communication wire and/or the power line. The toroidal coil is connected to the current detecting unit. The current detecting unit converts the current from the toroidal coil into a voltage and supplies it to a switching circuit. The switching circuit turns on an indicator light circuit to light up an LED of the indicator light circuit.

Abstract: Aincludes a connection terminal unit capable of connecting a telephone, a handset and a headset, a connection path selection switch capable of selecting a connection path depending upon the kinds of the telephone and the handset, and an audible signal generator which gives required information when a wiring is established by the connection terminal unit adapted to the telephone and to the handset by the connection path selection switch. Further, the connections of insulated conductors between the telephone and the handset are successively cut to search a state of connection where no voice is heard from the telephone.

Abstract: The present invention is to inform a state where a communication device connected to a communication wire and a power line is protected from a surge current. The toroidal coil picks up a rapid increase of current caused by a rapid increase of voltage which occurs in the communication wire and/or the power line, to supply the current from the toroidal coil to the current detecting unit. The current detecting unit converts the current from the toroidal coil into a voltage and supplies it to a switching circuit. The switching circuit turns on the indicator light circuit to light up the LED of the indicator light circuit.