I have had keys stolen, car has fiat alarm fitted, I still have one key and alarm remote control. I want to know how to programme the alarm so it will effectively ignore the stolen remote and only be operated by the one I have.
The handbook is not clear, but Im told that when I reprogramme it with just the one i have now, it will not recognise the stolen one, is that true.
Sounds too simple.

It can be done, a while ago I had to get my alarm reprogramed but at the time I only had one fob with me. Just to see, I tried the other one when I got home to see if it'll work and hey presto, it didn't.
Now don't ask me how to do it cause I got it done by the company who istalled that alarm. I don't think any special equipment is needed or anything.

Your fiat dealer will be able to programme your car with your remaining key (as long as you have the red one), so that only that key will work the immobiliser. Not sure about the alarm though.
You will also need the 4 digit PIN that came with the key (on your key card, or on the little stickers that come with the keys in the first place).