Abstract: Apparatus disposed at location of a key telephone system and associated with the system to produce a substitute signal and a substitute alarm in the presence of a ringing voltage when the system is deactuated. The apparatus comprises: an electrically powered lamp for displaying the substitute signal when a first voltage is applied thereto; an electrically powered device for sounding the substitute alarm when a second voltage is supplied thereto; a second source; and a circuit arrangement coupled to the first and second sources, the line, the lamp and the device. The arrangement, when the system is deactuated in the presence of the ringing voltage, produces the first and second voltages and applies same to the lamp and device respectively to cause the substitute signal to be displayed and the substitute alarm to be sounded.