my 2000 mitsubishi galant 2.0td alarm keeps going off?

My 2.0 td Mitsubishi Galant is fitted with a cobra alarm and it keeps going off. When I disconnect the siren under the bonnet it stops completely, usually when I did this before the indicators would keep going but the sound obiviously stopped. I am wondering if the siren unit is faulty, there was also very heavy rainfall in the area where I live over the last week and a half, can anyone shed any light on it for me please.