Its use as the title of a 1990s sitcom might make one think of high school and gigantic cell phones, but saved by the bell originated from boxing. A boxer getting pummeled is "saved by the bell" when the signal comes to end a round.
That phrase was used in boxing writing early in the 20th century, but by the second half of the century acquired a figurative application describe one who has been relieved from pressure or difficulty from an outside intervention.
"Rain in August meant we were saved by the bell and I expect an average German crop," [Stephan Barth] said, adding that along with U.S. crop there would be "sufficient market supply" although prices would remain high.
Reuters, 4 Sept. 2017