2001 T&C false alarms

How would I go about diagnosing the cause of the alarm going off for no reason when the doors are locked? The driver's side sliding door has become spotty in operation. The door will not lock/unlock with the auto switch on the driver's door or by remote. And the door will not open by the overhead console switch or the remote. Now, after locking the doors by remote or by the auto switch on the driver's door, the alarm will sometimes go off after 5-10 minutes, sometimes longer. We have had the alarm go off in the middle of the night, after the doors had been locked for quite some time. So, there is really no set pattern that we can determine.

And recently, when unlocking by remote, the alarm will go off for a few seconds or at least until we hit the unlock button twice.

Any ideas on determining the culprit?