I just had a brainstorm. I have an old weather station from Oregon Scientific. When doing maintenance on it, I noticed the rain gauge was a seesaw with a magnet, a reed switch, and a small 'self dumping water bucket.' Here's the deal, the reed switch is a 'dry contact closure' which is a perfect fit for the screw terminals on a triggerlinc. voila! you connect them, count the number of closures over time, and there is your custom rainfall amount! It is also wireless with a 50' range. You could also monitor sprinkler output!