Emergency shut off valve (for leaks)

Does this exist? This is the second time my Backflow preventor has blown while I was away from the house. Not fun to get home with an inch of water in the basement. I know I am an idiot for not blowing out the sprinklers yet, but that is beside the point. In the future I will do my best to get that done, but in the case that I am stupid again, does anyone know if something like this exists? (where if it gets wet, it closes a valve)


Thanks!
Ryan

Edit: I found this "Water Cop" system. Looks like the sensor might not be real happy sitting outside in the elements.

http://www.absoluteautomation.com/watercop/index.html

I've seen WaterCops setups that do what you want.