The Diversitech SOS (safety overflow switch) is an electronic device that snaps on to existing ¾” PVC condensate lines. The SOS senses when the drain line fills with water then locks out the compressor contactor. Switch features: No moving parts to foul up. Easy 2-wire connection to 24 volt contactor circuits Bright yellow LED shows trouble. Cycle power to reset. Ask for D1VS0S1.