key fob immobiliser?

the immobilser on my car does not respond to the key fob even though light on fob comes on when i press it. i have changed the batteries, but to no avail, had breakdown service out and they said there should be a plate to earth the battery in the fob which i have never seen in it before. used a piece of wire for a make shift earth into where he said it had broke off, and light doesn't even come on on fob now. is he right in saying its the fob?

paul abate
March 2010