What is the origin of the phrase "dead ringer"? I am told it is related to the rather hasty and premature entombment of sufferers of the plague, who when they regained consciousness, found they had been placed in a coffin. Realising this potential adverse consequence, a string and attached bell were subsequently placed with air holes in coffins so that those that were alive could alert the graveyard staff, hence the term "dead ringer".
I always thought it was to do with the fact that ringer is a term for something that closely resembles something else, while dead, in this sense, means exact. So dead ringer means a double for something or someone.