Meet the Toro Sprinkler System Timer: a water conservation device with a wireless range of 300-feet. It works by absorbing rain water to interrupt power to the valves. The Wireless RainSensor dries out, as does the soil, allowing sprinklers to run as scheduled. You can adjust the rain sensitivity from .125 to 1 inch. Its weatherproof receiver can be mounted indoors or outdoors. It is compatible with any sprinkler timer. Not too expensive either.