Citroen ZX Turbo Diesel - Problem with ZX 1.9TD alarm - caspeed

Just bought this car yesterday (L Reg). Remote locking/unlocking OK but when I start the car sometimes the alarm goes off. Not on unlocking car or opening doors, but when going to start the car. I somehow managed to cancel it but not sure how. The manual is not very informative. can anyone help

Citroen ZX Turbo Diesel - Problem with ZX 1.9TD alarm - Peter.N.

These are a bit prone to being upset if you open them with the key and close with the plip, or vice versa. Happened with my wifes once and went on flashing the headlights all night.