A flapper is provided in the main conductive fluid supply inlet line, and a permanent magnet is affixed to the bottom of the flapper. Adjacent to the flapper, outside the pipe, a magnetically operated switch is placed. Conductive fluid sensors are placed in or on conductive fluid dependent appliances, to determine the presence or absence of flowing conductive fluids. The flapper's switch and the conductive fluid sensors are connected in circuit with a relay, which in turn controls an electrically actuated valve cutting off or permitting the entry of fluids from the source to the inlet pipe. If the switch is activated, and one or more of the fluid sensors is not, within a predetermined time period, then the electrically actuated valve will cut off the entry of fluids from the source to the inlet pipe. If the switch and sensors are activated concurrently, normal fluid flow will be permitted.