Yep, bellbox/bellbox battery is probably faulty.

Even testing the external sounder via the test menu, will not test for a faulty bell battery.

The only test is to remove the Hold off voltage (remove power to bell)

If you leave the Hold off removed, it should only ring for 15/20 minutes max. and stop.

OK. What is the consequence of leaving things as they are? I have now tested the strobe and external sounder which appear to work if I fully arm the system and effect an entry without disarming the system. If the bell battery is faulty, it doesn't seem to matter for the normal operation of the alarm. However, if I attempt to test the external sounder by using the diagnostic codes via the keypad, nothing happens, i.e. the sounder will not activate. As I say, I can arm the system and leave the house in the knowledge that an unlawful break-in will activate the alarm. So I am obviously missing something about the purpose of the bell battery.

the bell battery purpose is so that if the bell is removed from the wall, cable cut, control panel attacked etc it can use the internal battery to sound. Else it would be simple to break in, knock panel of the wall and silence the alarm. It will operate, but so will a car with no doors etc it has an essential component failed

the bell battery purpose is so that if the bell is removed from the wall, cable cut, control panel attacked etc it can use the internal battery to sound. Else it would be simple to break in, knock panel of the wall and silence the alarm. It will operate, but so will a car with no doors etc it has an essential component failed

Ah! Thank you. Now I see its purpose.