alarm clock

WordReference Random House Unabridged Dictionary of American English © 2026

alarm′ clock′, 

1. a clock with a bell or buzzer that can be set to sound at a particular time, as to awaken someone.

• 1690–1700

Collins Concise English Dictionary © HarperCollins Publishers::

alarm clock noun

1. a clock with a mechanism that sounds at a set time: used esp for waking a person up