There are several. I have one as I mentioned in my comment: it's called a Phyn Plus. It works with and without sensors. I have some in strategic places like under the water heater.

It actually caught a leak, although it wasn't from the plumbing. It was rain getting into the chimney and dripping into a puddle in the boiler room that set off one of the sensors. I like the cable-style sensor they have -- it's like a 4-foot-long headphone cord, but the whole length is a water sensor, so if any part gets wet it goes off.