Ill PM you its location as I don't think its a good idea posting up how to enable/disable a 156 alarm on an open forum.
Too late mate, there have been posts before which can be found with a bit of searching
AJR - There are plenty of options for you so don't give up hope
however it is best to check that your alarm and central locking are working first!
If your broken key fob was the correct one for the car (i.e. the immobiliser worked with the key) then I can repair the circuit board, check it is working properly, and then can also transfer all of the parts to a brand-new key fob with an uncut blade.
So long as the immobiliser chip is the correct one for the car, this should sort you out.
On the off-chance that the remote circuit board is really stuffed then I can supply a new one - this would mean the car needs to be coded to accept it but this can be done by dealers (expensive) or independent garages (£30-£40) or even friends with AlfaDiag software.
It is even possible to open your 'valet' key and remove the transponder and transfer this to a 'proper' key with the remote function.
If you search on eBay for Alfa Key Repair you will find my listing (ZAKSYSTEMS). You can contact me from there if you are interested
To be fair, you can do most of this yourself but I have the parts in stock, tons of experience and I like to be able to help...