Based on some research, is the OEM siren located in the rear wheel well as the e90? Is it a data connection? Or is it a pos/neg it can be tapped onto? Would appreciate any ideas! Thanks

 

Yes it's located in the rear wheel well. It has 3 wires. Positive, negative and one data connection.
I also wanted to retrofit the oem alarm system, but didn't finished.
If you do that, please notify me.

 

Well.. I wanted to get a DEI alarm installed... and I didnt want that nasty ass DEI chirp.. i love the BMW one.. was wondering if theres anyway I can have that sound when getting it installed.... how did yours go?

 

I didn't install it. I just studied something about the retrofit.