That is true. Somehow it touched off a memory of what was done in the Middle Ages when there was no use of formaldehyde. Then, they put a string next to the body inside the coffin and attached the string to a bell on top of the grave. A person was assigned to stay at the grave site and listen. If the person was not dead he or she would pull on the string and the grave would be immediately excavated.
This practice is associated with an English phrase but I forget it (I forget a lot in my old age). Does anyone remember it?
OP, there are a couple of phrases, but some authorities dispute them:
“saved by the bell”
“dead ringer”
“graveyard shift”