Saved by the Bell

I don't know where the saying originated, "Saved by the bell." Perhaps with boxing. In my youth, it was the school bell. If one misbehaved, one was put out of class. If the principal passed by, and found that someone had been put out of class, they received a caning. When the bell rang, therefore, one was saved by the bell. OBSERVATION: I myself was saved by the bell. One tried to hide when the principal appeared, but not everyone succeeded.