Re: key fob
On my 'Y' reg GTV, The 'meta' box controls the remote locking. And I assume the alarm system because it does not work if you remove the box. The replacement Meta box and two key fobs comes with the red code card. This is different from the 'Code' system that recognises your key when you put it in the ignition. The 'key' related code system has a completelly different controller that matches/locks with the ECU. This is nothing to do with the code in the remote locking fobs.
You should have an M99T2 R.R.C car alarm central box. Black plastic with a red label. About the size of two cigarette packets. Behind the radio accesed from passenger footwell. These boxes were not on the wireing digram as, for a period I understand, they were added to conform to UK vehicle security rules.
It may not be on your car. My X reg Alfa 156 does not seem to have one.