Abstract: The flashing light, which is used by automatic telephone call distributing equipment to indicate that incoming calls have backed up and are awaiting service, generates voltage signals the frequency of which increases with the increase in the number of calls awaiting service. The voltage signals control several relays energized one at a time and successively as the signal frequency increases, and one such relay causes the emitter-collector circuit of a transistor momentarily to conduct each time the relay is energized and deenergized, respectively. Each time the transistor conducts it energizes another relay which momentarily energizes a bell chime to produce an audible signal.