Alarm goes off after opening door

I used to have a Ford Escort for a work vehicle. If you locked the vehicle with the fob the alarm would go off if you unlocked it with the key until you put the key in the ignition. If I locked the door with the key it wouldn't happen.

Try unlocking the doors with the fob and then only use the key.

What I do to lock it is by pressing the power lock button on the door when I get out. That have anything to do with it maybe?

Then when I go to unlock, I use my key to unlock and as soon as I open the door it goes off.

Basically 1 out of every 25 times of unlocking my door it does it, gotta say it is pretty embarrassing and annoying as hell. Usually scares the crap outta me because i dont expect it.

Comparing the two wiring diagrams one gets the impression that the alarm sounder is separate from the regular horns. Perhaps this is not the case?? Don’t have a factory alarm on mine to actually look at. Definitely don't cut your regular horns. Here’s the wiring diagram for the regular horns to compare to the alarm wiring diagram:

Ford Service Manuals - Wiring Diagrams

Ford Service Manuals - Wiring Diagrams

Note the black/light green wire to the "Anti-Theft Horn" while the regular horns indicate a yellow/light green wire. The regular horns should have some kind of quick disconnects on them. Just unplug them and set off the alarm to see if they're what the alarm uses.