Simply place the MS-WD2 on a flat surface under HVAC equipment, compressors, electrical switchgear, rerigerators, water tanks, dishwashers, washing machines or other potential leakage areas. When there is enough water or liquid to bridge the contacts on the base of the MS-WD2, an alarm is trigger which sets off the audible horn, LED and closes a normally open contact. Stand-alone 2-year lithium battery operation Solid-state relay used for remote sensing Horn is 10 seconds on followed by 30 seconds off LED is 10 seconds off followed by 30 seconds on No routine maintenance Battery included (readily available and easily replaced) 3" high x 2" wide It can detect a level as small as 1/16 of an inch. Can be used stand-alone or with the Antx TMxx monitoring and alarm systems.