A theft preventative system, such as which is specifically associated with high resale value metals employed in heating, cooling and ventilation (HVAC) assemblies. A first embodiment utilizes a transformer and relay arrangement creating a closed circuit through the lines of conductive copper pipe, via interconnecting wires, and which is also hooked to an alarm for notifying when the metal conductive circuit to the copper line is opened, either by cutting the copper pipe or the wire connected to it. A second variant discloses incorporating a fluid pressure switch into each of the copper lines, for notifying when fluid pressure within the line decreases, this indicative of the normally fluid filled copper line being sectioned.