Originally Posted by Erin
Presumably a float switch wired into an alarm sounder is all you need.
No help to the OP but vaguely topical:
MANY years ago I was asleep on a very small boat somewere out in the Red Sea. I was awoken at 0300 by "maintenance" noises and arose to find the skipper (Udo Fisher) poking around in the bilges.
"Notting, I hef vired ze ship's horn to zer float svitch"
"Ach, zer iss som vater comming in, und I vant to get som sleep.."
1. I slept (kinda) in my BCD.
2. She went into drydock two days later.
3. She was never relaunched.