I had the same problem with my '93' Jeep Grand Cherokee. I found that if I keyed my drviers door lock the security system would turn off.
I bought mine used & was told the driver's door would disarm the alarm. Huh!? It would go off at the worst times,we'd panic,try the door,try the ignition, finally pop the hood & disconnect the battery. I finally found the magic solution..... My tailgate turns it off! The trick to NOT set it off is... The driver is the last door to close before locking the vehicle. But if you forget & the alarm sounds, unlock the tail gate!