I installed a few. It had a plunger in one of the canvas snaps. We also put a pole with a Stobe in the poleholder and if it got pulled out it would trip the siren.
Its all low volatge and runs off the main batteries.
It's a pain in the A## to wire and do it neatly. The on/off switch was magnetic and placed in a certain spot, so to shut it off you held a magnet against the hull where the interior switch is placed.
Like I said, this was a while ago.