The "standard" BMW alarm on my 1995 6 speed was not Cat 1.
I bought a Cat 1 BMW alarm from "The stealer" and a BMW Technician mate fitted it for me.
The only change I saw in real terms was the single button BMW remote being replaced with another BMW remote, with one red and one grey button on.....and no keyswitch on the sounder unit........
Not sure if this helps.................
Mark