Definition of alarm bell
: a bell that sounds when an alarm is activated
—often used figuratively
… the Mexican swine flu outbreak that is sounding alarm bells [=causing people to become worried or alarmed] across the world …— Andres Oppenheimer, Miami Herald, 30 Apr. 2009 The spike in oil prices has set off alarm bells across the automobile industry.
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Merriam-Webster unabridged
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Time Traveler for alarm bell
The first known use of alarm bell was in 1548
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