One thing. If you want to take a wild guess and be lazy - just remove all those screws from the cover under the wipers, bend the cover up, and about midway between the passenger side of the car and the middle of the car, is the alarm siren. Unplug the three wire cable going to it and see if that fixes the problem.

If so, leave the thing unplugged, if you want an alarm siren, order a new one.