Brian:

I don't know if this is code compliant in your area but Uponor (use to be called Wirsbo) makes a residential system that is part of your home plumbing system. It's a pex pipe system so the labour to install it is less than the normal iron or copper system.

I have seen it installed here in the house of a plumber as a retrofit after his house had a fire.

Here is a link to the cut sheets for it. http://www.uponor-usa.com/index.php?id=122&pid=29

The only downside I can see with this is if it does activate, you would be charged for the water that passes through the water meter. I think, but am not sure that sprinklers if dedicated are not metered.