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.