Lead cups were used to drink ale or whiskey. The combination would sometimes knock a person out for a couple of days. It was not uncommon for someone walking along the road would take them for dead and prepare them for burial. They were laid out on the kitchen table for a couple of days and the family would gather around eating and drinking to wait and see if the person would wake, hence holding a "wake".
England is old and small and they started running out of places to bury people. So, they would dig up coffins and would take the bones to the house and reuse the grave. When opening these coffins one out of twenty five were found to have scratch marks on the inside and they realized they had been burying people alive. So they thought they would tie a string to the wrist and lead 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".
(all images taken from the internet)
I didn't take the bother to verify any of these facts and this, the final post of this series may give some cause to speculate a little. I mean, being out cold for days just by drinking from a lead cup? And one in twenty five is a pretty high percentage. Knowing that would make anyone afraid to die.