Citroen ZX 1.9D Sx 1996 Alarm Problem?

After letting the battery go flat the alarm is proving a big problem, going off intermitently sometimes when I open the door to get out sometimes as I shut the door after getting out, but not every time.According to my owner's manual there is supposed to be the facility to deactivate the alarm by use of the ignition key in the alarm cover which is supposed to be found behind the R/H headlamp-it ain't there- Can anyone help please?