Alarm problem

Hi everyone. I have a problem with the alarm. Occasionally (getting to be frequently) the alarm will not turn off using the fob. Can be very irritating sitting in a car park continually pressing the button and watching nothing happen! The central locking will still work using the key, but obviously, open the door and the siren starts! Put a new battery in the fob but no different. Can anyone help?
Thanks

Doris you don't tell us which Disco you have.

Its a 1997 TDi.

I had a similar problem with my 98 Disco, it turned out to be a faulty siren once I changed it was fine.
All I will say is if possible borrow one from a friends disco and try it first as they cost about £80.

Trevor.