Sprinkler Daddy Says:
Turn your sprinklers off automatically when it rains!

Rain/Freeze Sensor For Your Automatic 
Underground Sprinkler System

A rain/freeze sensor is a little gauge that attaches to your eaves trough.  Your rain/freeze sensor can determine when you've got rain or freezing temperatures and send a signal to your timer to skip the next watering cycle.

The sensor can be adjusted to react to anything between 1/8" to 1" of moisture.