All 3 series BMW's including the X3 doesn't come with the alarm system installed. It is pre-wired but is dealer installed option. Just the same that all 3 series cars don't come with floor mats... It is my understanding that all 5,6,and 7 series cars come with the alarm system installed. Although you would think that at $32 - $42k car would come with an alarm and floor mats.

The alarm system should run you about $400.
The Universal Garage Door Opener will run you about $800 on the X3.