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The Greeks invented the first prototype of an alarm clock around 250BC. This prototype was a water clock but when the rising waters reached a certain point, a mechanical bird would be hit which triggered a whistle.
In 1787, Levi Hutchins of Concord, New Hampshire invented the first mechanical alarm clock but it would only ring at 4:00 a.m. It took another 100 years before an alarm clock which could be set for any time was invented. This invention was patented by Seth E Thomas.