Broken keyfob

Anyone have experience of diagnosing or fixing keyfobs?

Car was bought new with two keys. The key I always used broke a little while ago. As I have another, I just chucked it into a drawer and used the spare.

The problem with the car last week caused me to reassess the situation. It would be very useful to have a know-good 2nd key!

The radio part of the key that works the alarm seems broken. The LED in the keyfob blinks when I press the buttons but the car doesn't unlock/lock.

I've tried recoding it by the "insert it into the driver's door" method but that doesn't work. I assume something has gone awry with the electronics.

I can open the car with the key and start/run the car with it.... I think. Haven't tried it in anger yet as it's still early morning and I don't want the alarm going off annoying the neighbours too much.

Has anyone used the "XBOX 360" method to fix a knackered keyfob?

J.