My car was open with engine off and i left it for 5 mins. So I was about to leave my mates and I couldn't knock the immobiliser off. I can't even lock the car with the fob if I wanted to 
Left the car at his over night. Phoned the guy up who installed it about 2 years ago and he said thats very strange and he has never had any problems with them. The only thing he can think of he said is it might have blown a fuse or the battery gone in the fob. Tried my spare fob and still nothing.
He's coming out tonight to have a look!