It’s interesting you mentioned this — I am working with a friend on a ESP8266-based motion sensor (it uses a PIR motion sensor, which is very common), for a different application, but it can probably be used together with OpenSprinkler using a simple API. The main technical issue we are trying to solve at the moment is that the motion sensor seems very sensitive to ESP8266’s transmission resulting in false triggers from time to time (though it can be easily solved by moving the motion sensor away from the ESP8266 chip).