Abstract: An adapter alarm for boats for theft prevention. A multiple number of spaced brackets attached to the gunnels of the boat, and an automotive alarm plunger switch actuator is secured in each bracket and wired to a key operated alarm unit that is battery operated. Engaged with each plunger switch actuator is a split-edged clamp that is force-fitted to the shaft of the plunger and which is secured by a cord to a hook attached to the boat covering canvas. The circuit is wired to the plungers in the brackets and when the canvas is disturbed the clamps release the plungers which close the circuit to the alarm unit aboard the boat.