OEM Alarm systems on BMWs are not advisable.....I've seen it time and time again....before you consider adding it to your vehicle....think about the consequences if your BMW doesn't work quite how you bought it.
We had a manager from Circuit City come in with her Z4. She said the passenger door wasn't locking. We traced it back to her OEM alarm system that her employees installed, incorrectly on her BMW might I add.
We had to uninstall the whole alarm system and re-program her car. It took us a couple days to get things working again because her alarm system fucked up the car. Luckily we have very smart BMW technicans that can handle situations just like that.
Next time it was in, the doors were working and no OEM alarm on her vehicle.
Think before you make a move, that's my advice.