England is a small, old country. Soon they started to run out of places to bury their dead. So they would dig up coffins and take the bones to a bone yard and reuse the grave. When the coffins were opened 1 out of 25 had scratch marks on the inside and they realized people had been buried alive. So they would tie a string around the wrist of the corpse, thread it through the ground and tie it to a bell.
Someone would have to sit at the grave site all night (the graveyard shift) to listen for the bell, thus someone was “saved by the bell” or was considered a “dead ringer!’