If you were buried alive and woke up, your movement would trigger a hidden mechanism inside the coffin. This would launch a shiny ball into the air and ring a bell as a warning. At the same time, a valve would open, letting in fresh air and light through a tube. This tube also carried sound, meaning you could yell for help to cemetery workers. But actual dead bodies can release gas and move on their own, meaning the alarm could be triggered by a dead body. resulting in real corpses being dug up. Which is why this invention never really caught on.