Scantronic 9448?

The external alarm went off in the middle of the night, although the alarm was not set. I replaced the battery in the box in my cloakroom but the tamper light remains on and when i type in the reset code it beeps and does nothing. the code will stop the alarm sounding when i open the box but it cannot be set to on and if i leave it the external alarm goes off again. the only way i can then stop it is to pull a plug on the battery
i have read things like linking this to that but have no idea what this means.....?????????