Science has come a long way since the dark ages. While there a still new discoveries to be made and disbelief in some already proved discoveries, it is undeniable that science has made modern life much more easy and comfortable than ever previously imagined. One of the biggest boons science had provided to was the advancement of the health industry. After all, we are all living loner and healthier lives thanks to science, but things have not always been like this.
In the very distant past (think medieval times), way before vaccines had been invented and debated about, health care was extremely primitive and inaccurate. Besides the well-known use of leeches and blood-letting as a common "cure" for many maladies, the tools doctors used were as crude as their methods and solutions. Their lack of advanced technology made it very difficult to accurately pinpoint symptoms and illnesses. However, the greatest danger of such a lack of health technology did not harm the living so much as it harmed the comatose and seemingly dead.
The first heart monitor wasn't invented until 1977, and, until then, doctors had to rely on less advanced methods to determine whether or not their patient was still alive. But humans aren't perfect beings and are prone to misjudgments. As a result, many people in the past were buried alive because they were presumed dead. This, obviously, was a problem. If someone were to one day wake up and find themselves buried six feet under the ground, they would be hard pressed to find a way out of their coffin. Of course, a solution was found. When burying the dead, a bell would be attached to the fingers of the deceased, so, if they turned out to be still alive, they can just ring the bell and be dug out by the grave watchmen.
Death is a very common fear nowadays, but in the past the fear of premature burial was also very rampant. No one wants to waste away their last waking moments in a coffin when they can be dug up, thus safety coffins with bells attached enabled the people buried to early to return to the world of the living.