alarm

fear resulting from the awareness of danger

a device that signals the occurrence of some undesirable event

an automatic signal (usually a sound) warning of danger

a clock that wakes a sleeper at some preset time

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"

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"