Abstract: A system and a method for the detection of a water leak. An alarm can be sounded and a valve closed to shut off a water supply when a wireless sensor is in the presence of water. Exemplary embodiments of the wireless sensor can be battery supplied and mounted to a wall or a floor. In fact, a magnetic latching valve can be used to minimize power consumption, and allow the entire system to be battery supplied as needed. Wireless sensors according to the present invention can be disposed in homes or commercial buildings, including, e.g., under hot water tanks, sinks, A/C drip pans, ice makers, washer machines, and/or toilets.