Few days ago after only 2.5 years of owning a car from brand new, I had problem with one of the keys, switch for trunk stopped working. Unfortunately it was not only battery, since it is obvious by pressing the switch, it feels like it's not there any more.
I have found the repair manual - Michaeld's Button Flip Key guide on the http://www.alfa156.net/
and using it I have repaired the key. The problem was in the switch itself, it has fallen off the circuit board.
Just to be sure I have glued all the switches with super glue, and soldier it again, and now everything works OK.
Please note (if you read the manual) that is extremely hard to open the key (and I am first owner of the key, it was not glued before), it had to be cut.
Also, one more VERY
important thing: it is not mentioned in the manual, but there is a small glass ampule with a coil, under the circuit board, near the round part of the key blade. I did not know it was there and it fell off on the floor when I opened the key using cutter and strong force. I was lucky not to break it or to loose it because it is a coding device for Alfa code - I think you can use the remote, but you can't start the car without it !!!!
I will also post some additional pictures later in few days when I download it from camera.
Best luck in repairing!