Hi Alan
You can unlock the car with the key without the alarm going off, it does disarm the alarm, but only on the drivers side and is still ok to drive.
I had a Rover 200 with same problem, changed the battery and was ok... try to give the key fob inner conections a clean to maybe get any underlying dirt of the terminals.
This should then work..
Sounds a silly question, but have you put the battery in the right way.?
Hope it helps
Marie, December 2008