Hey Reno,
I'm pretty sure I've such a thing. Search the internet "flood sensor." It is basically a little alarm with a small cord running to a sensor mounted near the floor. The "sensor" consists of 2 metal prods that are in contact with the floor. When water flows between the two prods the alarm goes off. Not sure if it works or not. I remember seeing it on "Ask This Old House." I think it's pretty inexpensive too, when you compare it to remodeling a basement.
We use those at work for early detection of flooding under the false decking of server rooms. They work very well.
