The problem with your alarm is that the back up battery is needing replaced you can purchase one from B&Q (2amp rechargable)
You will first have to power the system down mains and battery and then re power on battery first you may find the system may not take your old code if not try 1234 or 0123 to silence refit lid on control panel and press reset
to input new code if returned to factory code press prog key then existing code then number 8 then new code then reset reset Battery should be changed every five years
ps if the module in your outside bell box is ok the outside box will activate when the battery and mains power is removed
Darren
January 2008