An absolute moisture sensor is coupled to a controller circuit with the combination being integrated into a single device as a moisture-activated switch. The resultant switch is coupled in series with a power control line of a moisture-controlling device and can be placed within the medium for which moisture is to be controlled. In one typical use, the switch is buried in soil for control of valves that supply irrigation water. Since the moisture sensor is selected to provide an absolute reading of moisture, the switch programs itself when power from an external source is first applied. A communication protocol provides for readout of sensor values and allows for a remote reset of the controller.