I was required to install a high bilge water alarm as a result of my last insurance survey. I used a bilge pump float switch and located it just under the cabin sole. It is connected to a radio shack alarm. Works great, is cheap and I hope it never, never goes off except when testing it.

What is very valuable to me is knowing if the bilge pump is running and how frequently. In that regard, I have a red light in the cockpit hooked up to the red light in the cabin that goes on when the bilge pump is running. In that way, when sailing, I can see if there is a greater frequency than normal of bilge pump activity.