Odd alarm behaviour?

The 2001 Rover 45 Impression we recently acquired seems a bit odd with the alarm/immobiliser mode of working. Unlike the MGF's the chiming does not work and one does not have to press the fobs button if the car is unlocked and left for a while.



But on occasion the chimes cuts in then out with no fob buttons being pressed. As I am not familiar with the 45's systems how is it supposed to operate please?



We only have one key and fob so another will be required and sorted out but if we have a problem with the system it's seem logical to get it all sorted at once.

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