Due to recent close call of neighbors boat I am installing a High Water Bilge Alarm. Probably a Rule 33 ALA.
I see the alarms that will call you but they are very pricey and the complexity also makes me shy away as the more complex something is the more prone to failure.
The issue I have with the common alarm like the Rule is they only notify the interior of the boat. Our houseboats sit empty mostly. I guess I could rig an outside alarm/light?
I'm thinking of adding a simple mercury switch attached to an alarm outside. First thing pops to mind is a strobe/alarm for fire. Just plastic coat blue and relabel.