England is old and small and the local folks started running out of places to bury people, so they would dig up coffins and would take the bones to a bone-house and reuse the grave.
When reopening these coffins, 1 out of 25 coffins were found to have scratch marks on the inside and they realised they had been burying people alive.
So they would tie a string on the wrist of the corpse, thread it through the coffin and up through the ground and tie it to a bell.
Someone would have to sit out in the graveyard all night (the graveyard shift) to listen for the bell;
thus someone could be, ''Saved by the Bell'' or was considered a ''Dead Ringer''.