Abstract: Ringing current is a high-voltage, low-frequency signal which is sent from a telephone exchange via a pair of wires to ring a bell in a distant telephone. It is becoming common practice for distant telephones to be connected via a carrier connection and the present invention provides a device for conveying a high-voltage low-frequency signal along such a carrier connection. The device comprises a sender part and a receiver part connected together by the carrier connection. The sender part on/off modulates one of the carrier frequencies used in the connection at twice the rate of the low-frequency signal. The receiver part detects the on/off modulation and uses it to connect alternate opposite voltages delivered by a voltage multiplier circuit to a line connected, for example, to a telephone bell.