Bell box is not the issue mate although just to add i despise this sort of alarm gear 21 years ago veritas were a tolerable panel, didnt mind installing or buying but since 2000 they have tried to modify the panel way to much
Check sensor lids/ window sensors, check door contacts and panel on lid if no luck remove panel lid, loop tamp press the pcb tamper spring if tamper clears ur a winner if fails get a engineer in
Nick, August 2016