you have to get under the hood with a set of diagnal cutters or side cut or some kind of cutter to cut the wire to the siren if that is the problem. there is two wire that lead to the siren one red one black on most. just cut them bolth and make sure you can resplice it. this is if it has been being anoying like going off all the time this mean you may need to get under the hood wile it's going off.
sorry for the pause i had to eat dinner. just be carefull if you had the anti car jacking type module installed it will still trigger it but will shut the siren off. if you cut the wire to the siren. so if your car does not start it the patts or car jacking module. that mean it will have to be reset it to start and drive it any were. if it has the remote start you most likely have a patts module. any ways good luck alarms can be a pita.