Why would 2007 Skeeter21i alarm activate while boat not running?

[BabyBrushog]

An alarm went off (out of the blue) while my boat was sitting in my enclosed garage. Had the boat on the water on Tuesday and Wednesday. Put it in the garage Wednesday evening, plugged in the onboard battery charger. Friday morning around 9am, heard the boat horn begin to sound. It would sound for 5-10 seconds, then stop for 20-30 seconds, sound again, stop again. Off and on for maybe 6-7 times. Took a few minutes for me to figure out it was my boat making this sound. Once I realized it was the boat, I unplugged the charger (actually unplugged it during the alarm and the alarm continued a few more seconds). I could smell a very slight electrical burning smell under the console. No heat. The final alarm sounded for maybe 15 seconds and slowly faded. Then it never went off again. One other note, after all this, my horn no longer works.
Any ideas why this alarm (which sounded like the boat horn) would just go off suddenly with no activity around the boat or in the vicinity? No animals in the garage. Battery compartment did not have any smell, no heat in the compartment, batteries were charged, all green lights on the onboard charger. I’m open to suggestions! (Yahama 250 VMAX HPDI motor)

 

[Grub54891]

Apparently something shorted out. Good thing you were there to catch it before it started on fire. The first thing to do now is to disconnect the battery. Then get under the helm and look at the wiring for any melted wires, or funny looking connections.
follow the horn wiring starting at the horn, follow it back to the harness and I bet you find the issue.

 

[Texasmark]

Most alarm devices are fed with 12v from the ignition switch being in the ON or START positions......some key assemblies may have a preceding INST/ACCESSORY position where power is applied. Two things have to happen for the alarm to sound: You need to have power switched to it and you have to have ground (batt. -) connected, simultaneously. If your alarm device is wired directly to 12v then you only need to ground the low side.

Having the boat sitting at rest is very confusing as if mice or rats have been at work, one would expect if it shorts it will stay shorted, a solid alarm till it burns the wires in two or the fuse blows that controls that powered circuit....if there is a fuse.

One other possibility would be that the rodents have done their dirty work and are actively moving around in the area...like having a nest under your console sort of thing. Just some thoughts.