IMO stay away from add-ons like the one you describe. They can trigger untold problems in computer sensitive 7's. As previously posted the car has several anti-theft devices that even insurance company's like.
Good - Fast - Cheap: Pick any two.
E23 735i; E30 318i; E32 735iL (X 2 - 1 White and 1 Light Blue); E34 535i; E38 735iL; R50 Cooper; R55 Cooper Clubman.
E21 318i; E32 735iL; E34 535i; E38 730iL; E53 4.4i