My 02 has that problem when sun on windscreen I lock van with drivers door open, by pressing lock button on dashdoard, then shut and lock drivers door with key. Van locked up without setting alarm.
I have pluged in diagnostic code reader and cleared all codes none had anything to do with alarm and it still sounds!
Next I will unplug inside sensors one at a time and let you know how I get on Andy
Andy
July 2008