They are factory fitted Thatcham Category 1 alarms which have both volumetric (internal) and perimetric (external) systems. The key fob has an inbuilt transponder coded to the car.
I don't think you will be able to add to the existing system as it is linked to the BCU which would then need recoding. You would, of course, be able to fit an additional system but that may not add anything to the existing security.
Hope this helps, good luck with your search.
Nich.
Nicholas John Peter Tinker - # 484
Manufactured on Tuesday 27th April 2004 @ 12.17.47.
Commission Number: 24468.
Brochure Model: M3 Tourer 4.6 V8 260PS.
Specification Code: L01B.
CICode: D1511.
Trim Level: TL8.9 (M3).
65th ZT-T 260SE to be made out of 115.
11th ZT-T 260 SE in Pearl Black (PBT) out of 23 produced. Manufactured in the UK by MG Rover Group Ltd.