Abstract: A device for detecting the presence of excess moisture, water or other electrically conductive liquids in a given area which includes a visual or audio warning indicator. The device is characterized by non-complex, miniaturized circuitry and a housing that is mounted in a standard 115 Volt conventional, electrical outlet. A detachable liquid sensing unit includes a cellulose pad having a pair of electrodes embedded therein, encased between perforated sheets of plastic film with a connecting conductor having a phone-type jack which plugs into the power unit housing. The power supply and gate circuit includes a step-down transformer with its secondary connected to an alarm actuated by a thyristor which is made conductive by current flow between the sensor electrodes, the current being conducted by the presence of liquid in the sensor pad. The low current and voltage of the device allows it to be safely employed in a home or commercial environment without danger to persons in the vicinity of the device.