Car alarm fault on Rover 45 2005 model?

Quest: 11 July 2009, Car alarm fault, on Rover model 45 2005. Over the past two weeks have a fault which is getting worse, that is after you have immobilised the alarm off the fob, you open the door and it goes off. You can stop this by mobilising and immobilising the alarm straight away. Note that when you mobilise the alarm, the red neon light will flicker instead of flash, is this ttying to tell me something.....