Abstract: Apparatus for indicating if any one of a plurality of sensors detects a malfunction in a heating and cooling system. In response to a sensor detecting a malfunction, a local alarm coupled thereto, a common alarm coupled to all sensors, and a telephone dialing and message conveying device are activated. Signals provided by each sensor to a single coil that activates the common alarm and the dialing and message conveying device are prevented from being conveyed to a local alarm coupled to another sensor by including the coil in a rectifier bridge arrangement. If a malfunction corrects itself or is corrected, the local alarms and common alarm are switched off and reset to permit indication of a subsequent malfunction. The dialing and message conveying device, local alarms, and common alarm can be selectively inhibited. In the event of failure of a primary a.c. power source, a d.c. source is automatically activated to provide power.