Definition of "Alarm" :

noun: a device that signals the occurrence of some undesirable event

noun: a clock that wakes a sleeper at some preset time

noun: an automatic signal (usually a sound) warning of danger

noun: fear resulting from the awareness of danger

verb: warn or arouse to a sense of danger or call to a state of preparedness

"The empty house alarmed him."

verb: fill with apprehension or alarm; cause to be unpleasantly surprised