A bell with plastic lid can a have pcb with track which forms a 24hr circuit like cc wiring
A metal bell can a have circuit made between inner & outer cover which is completed by the drill bit
if you want a panel battery-
https://www.securitywarehouse.co.uk/catalog/intruder-alarm-c-36/intruder-alarm-ancillaries-c-36_46/pyronix-battenf8xaa-battery-for-enforcer-32we-homecontrol-p-5345.html