Here is my report on an installation on my E90 2008 328xi:
1) Did not disconnect the batteries.
2) I did the installation backwards starting with the horn on the wheels. Did not remove the wheel since there was enough space to work with. I did use my homemade ramp to raise the rear wheel to get better workspace underneath. The hardest part for me is removing the wheel cover since I did not remove the wheel. Also, I initially thought that the horn and car's wiring harness did not match. There is a plastic adapter on the car's wiring of sort that I just snap out and exposed the perfectly fitted plug for the siren/horn. Whew! I thought I have to call Tischer's (bought the Alarm from them) and complain about compatibility.
3) The alarm module inside the car was a breeze to install. Just open the overhead cover and plug it in.
4) The hood switch was also a breeze. The newer E90s engine compartment alarm wiring is already laid out, all you need to do is install the hood switch bracket and actual switch then just plug the connector (also comes with the plastic adapter that I snapped out). No need to remove the reservoir.
-Clown nose blinks right away on arming.
-Interior motion sensor also worked - this set the alarm off
-I haven't tested the hood yet.
No chirp yet - (this is the feature I wanted the most for audible lock confirmation!)
I called my dealer for a programming and quoted me around $80! They won't commit to actual cost since they are saying that programming might take longer. Duh? I don't have iDrive, no nav, no premium package and non of the other options - I wanted the car for its performance. I'm bringing it to them in the next few days for the activation. I'll post the result after once it is activated.
BTW, I love this DIY post. I wouldn’t have attempted the installation without this post. Hopefully everything works out fine after the activation.