Like we sometimes set up a thermostat to close a switch on a signal light(in a visible window) if temps drop close to freezing in a house that is not used in the winter. Allows someone to see from outside if there's a problem before the water pipes burst.

Lobster boats sink more in the winter (it seems) mostly because people don't get onboard often. You could see a light on a moored boat, especially at night, that signaled the bilge pump is on, even from a distance. Alarm would work up to a certain distance but I'm sure that would run the batteries down more quickly than an efficient bright light.

There are cell phone gizmos too but this would be a cheap alternative.