How exactly does the factory alarm on a 190 work. Sometimes it will go off when I open the door and to turn it off I need to unlock the trunk. I have no idea what I did to activate it though so any info on the system would be greatly appreciated.Thanks

One my '88 the alarm is activated when you lock the door, and deactivated when you unlock the door.

You can test by locking the car with the drivers window open, then open the door. The horn should beep intermittently. Close the door and turn the key in the unlock direction to deactivate the alarm.

Duke

You can only shut the alarm from the front passenger door. Don't ask me why but those werer the instructions I received when I bought the car.