... been awhile since I had one apart, but inside the door are several elecrtical components of the alarm and automatic seatbelt system.
iirc, there's a pin/microswitch/magnetic dingus that senses the lock cylinder rotating, and that's what sends the alarm module the "authorised" signal that disables/turns the alrm off so the door can be opened without triggering the alarm.
I've seen a few of those knocked loose/floating, just waiting to be reunited with the mechanism.
rememeber, the interior door panel/door card is removed by getting all the hardware out, and then pulling up, not out!
If you don;t find anything amiss inside the door, another place for problems to occur is teh wires themselves inside the flexible boot that passes from the doorframe into the body. A good place to look if you;re having other problems like in-op windows/doorlocks. The constant opening/closing of the doors flexes the wires, and on high mileage cars, the wires finally fatigue and begin to break strand by strand, untill finally, there's not enough wire strands still connected to allow things to work properly.
One final place to look is in the door/body harness connector, (ircc, it's easier to get from outside the car by removing the boot in the "a" pillar, and then pulling the connector out where you can work on it ... lot's of stuff in the way to try and get it from inside the car) Water from a a bad door boot/leaking windshield has corroded more than a few of them, leading to in-op door circuits.
If any of you guys do troubleshoot this and find the problem, please take pictures and report back what you find.
... be nice if someone searching this subject could find a thread where someone reported the resolution/fix, (with pictures!)
thanks!