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?