Mystery switch

We still don't know what the mystery switch is? You say it has an (aftermarket) Thatcham alarm fitted, but haven't seen it but have set it off. How do you know that?/Do you have an invoice for it? I ask the question as the car does have a factory alarm on it?

Ive got bills from 2001.
the sterling touch cat 2 immobiliser was fitted in 2005. that is the small square on the dash, will not start unless the fob is used.
I have set the alarm off once, dont know how.
from bike experience, you have to dis activate the alarm if you remove the battery or the alarms own battery thinks you are trying to steal the bike same thing if the battery gets too low . But, on the car, the battery has been going flat on and off for a while and the new battery also went down. This I assume to be due to the Bose speaker unit has not been removed for the after market radio. Only saw this on the cutaway youtube series. Car is now on Optimate.