I looked into this extensively a little while ago. ESD = Electric Shock Drowning
People don't realize that the worse case combination for ESD is fresh water and AC shore power.
Here is one of many links:
https://www.electricshockdrowning.org/esd--faq.html
Lots of information and other links here:
https://www.electricshockdrowning.or...resources.html
a link from Boat US:
https://www.boatus.com/seaworthy/mag...-explained.asp
A link from the ABYC:
https://abycinc.org/blogpost/1678504...u-Need-To-Know
Unfortunately, the experts suggest that there be no swimming near any marina that has shore power to boats as the only safe choice.
Alarms and detectors give a false sense of security, and only help if a pre-existing issue is in place before you get into the water. They don't help protect swimmers if a fault occurs while people are in the water.
Consider this, if you are at a dock with shore power, and someone is in the water, what will happen if a shore power cord is dropped into the water by accident. Bzzzzz! ESD.
What happens if an electrical failure occurs just when a battery charger turns on, or a refrige or A/C unit energizes, or a hot water heater turns on while swimmers are in the water. Bzzzzz! ESD.
A detector in these cases turns into a 'Electrocution indictor" instead of a warning to stay out of the water.
People in the water hearing an alarm, or feeling an electrical current or any problem will try to swim towards the dock and apparent safety. In reality, they may be swimming towards the electric field and that tingling that they are feeling or alarm that they hear could end up as ESD.
Now some say they have been swimming around docks and boats all their lives and never had a problem. Other's will say a GFCI or ELCI will protect you. Perhaps. But the experts say it's not worth the risk.
What if it's one of your family members that is hurt?
I suggest to educate each boater and each person at any dock where shore power is available so that they are well aware of the dangers. Then let them make their own educated decisions. Many marinas institute no swimming policy's from their docks where shore power is available.
But I wouldn't suggest one of these alarms after reading the background information on them. I agree that they can give a false sense of security. They could fail.
But other's think they are good enough for their lives and the lives of their family.