Did your alarm go off spuriously or did it go off because it was set off by motion it is suppoesed to be set off by?
I have intermittent problems with the alarm in my 350SD (it goes off when we use the key in the door sometimes or someone opens one of the passenger doors before the driver door is opened, neither of which should set it off) and the way you get it to shut off is to use the master key (squarish black end) to open the doors and then lock them. Sometimes that does not work I have to start the car, shut it off and then lock it. The dealer suggests this is a fault in the driver door lock where some essential part of the system is located. To fix it is several hundred dollars, and I have elected to live with it. If it gets workse, I may just disable the system.
Hope that helps. Jim
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)