High water alarms can help but only if there is someone to hear them or someone to do something about it.
Years ago we pulled into a small marina in Hampton, Va for the night. About 2:00 in the morning the high water alarm started going off on an adjacent and unoccupied boat. We were probably the only occupied boat in the marina.
I couldn't sleep so I got up to investigate. The boat was down about 6" but didn't seem to be taking on water fast. There was no one at the marina and no emergency phone number available. So I called the cops on my cell.
A few minutes later the cops showed up at the marina's gate but couldn't get in because it was locked. I had a conversation with them over the fence. They didn't have any way to get in touch with the marina's management either. We both decided to say f$#@ it.
The alarm stopped an hour later (maybe the battery ran down) and I got to sleep. We left early the next morning so I don't know what the outcome was but I left a message on their machine about the alarm. At least the boat was still floating when I left.
David