alarm clock, alarm -- (a clock that wakes a sleeper at some preset time)
Overview of verb alarm
The verb alarm has 2 senses
dismay, alarm, appal, appall, horrify -- (fill with apprehension or alarm; cause to be unpleasantly surprised; "I was horrified at the thought of being late for my interview"; "The news of the executions horrified us")
alarm, alert -- (warn or arouse to a sense of danger or call to a state of preparedness; "The empty house alarmed him"; "We alerted the new neighbors to the high rate of burglaries")