There is an ultrasonic sensor installed over head in the interior cabin. The alarm module and siren is an integrated unit located in the drivers rear fender liner at the top. The tilt sensor is built into the module/siren unit. In some slightly older modules there was a tilt sensor installed inside the right side trunk. And the final part of it is the hood switch although most cars already have it.
+ Coding of course to make it beep/flash, idrive menu's etc..
Edit: Not sure on the E93 other than the coding