I park my car and locked the door, after about 1hr alarm goes off. how to fix it on 2002 Mercedes-Benz SLK320

When the rain the car is wet it happen, but not happen when it dry

Asked by for the 2002 Mercedes-Benz SLK320
I recommend for you to have a qualified shop scan the car for stored codes in the alarm module. A know problem with that model is that the alarm module located in the trunk of the car gets wet and could cause the problem you are experiencing.
hope this helps.