An early prototype of the alarm clock was invented by the Greeks around 250 BC. The Greeks built a water clock where the raising waters would both keep time and eventually hit a mechanical bird that triggered an alarming whistle.
The first mechanical alarm clock was invented by Levi Hutchins of Concord, New Hampshire, in 1787. However, the ringing bell alarm on his clock could ring only at 4 am. On October 24, 1876 a mechanical wind-up alarm clock that could be set for any time was patented (#183,725) by Seth E Thomas.