Abstract: This system employs the standard single line tone dialing telephone instrument, connected via (typically) existing 4 conductor 22 gauge wire. A telephone hookswitch sensing circuit provides a trigger to connect a tone decoder across the talk path for a period of time established by a time delay circuit. When the instrument is tone dialed, the output of the tone decoder is fed respectively to: a gate circuit which switches the telephone instrument from the local intercom battery to an outside telephone line; a HOLD feature circuit which places the outside call on HOLD; a remote control circuit which turns on and off devices remote from this system; or to individual bells of other instruments within the system.