Why does the Alarm sound shortly after doors have been locked using remote key. on 1998 Mercedes-Benz ML320

This problem has started just recently and it now occurs every time the car is locked. I have tried using differnt remote keys to lock the vehicle but the alarm is set off each time.

Asked by for the 1998 Mercedes-Benz ML320
sounds like you may have a faulty door ajar switch,or trunk,hood switch.
You were correct. My rear passenger door lock has a faulty switch. Thank you for your help.
Your very welcome!