Door lock and Alarm

[Grant Dion]

Hi
I have 91 200tq. It's cold in Colorado today, 25 degrees this am. I unlocked
my driver's door today and got into the car, shut the door and then the
alarm started going off, right after I shut the door. I put the key in the
ignition, alarm still on, so I got out locked the door then unlocked it
again. The alarm turned off. It did this again, same results later in the
morning. I am guessing that the door lock sensor or something similar is
failing. Has anybody experienced this? If so what do I need to do so the
really bad trombone playing alarm does keep coming on? 
Thanks
Grant in Colorado Springs