This is no more than a well encased magnetic switch with a magnet in a float to activate the switch. Unfortunately, if the valve is "pulse controlled" as those in the timers I have are, then this sensor might not allow the pulse which turns off the water to actuate. An example of this is that I installed the sensor near the sprinkler in the hope that if there was some rain prior to the sprinkler coming on the sprinkler would shut off when the soaking was complete. However the magnetic switch opened when the water reached the proper level and the sprinkler continued to water the lawn until I noticed that it hadn't turned off several hours after it was supposed to(no saving water that time). If your timer will shut off the water when the sensor circuit opens then this will work as expected. If a polarity change in your timer opens and closes the valve then this device could be modified with a diode to perform as expected. However if a pulse of the same polarity opens and closes the valve this is not what you want.

works fine