Hi, and welcome to the Seadoo forum.
Well you could just disconnect the beeper, it's inside the handlebar cover, but I would suggest finding out why the constant alarm. The first circuit I would check is the temperature, start by disconnecting the green wire from the sensor on the head, it's near the pto side spark plug, if the sound stops you have a bad temp. sensor, or your ski could be overheating, if not post back.
Lou
Sorry I just noticed you have an Islandia, so the above info. really doesn't apply, moving this to the Merc. Powered sport boat section.