Definitions of alarm:

• noun:   a device that signals the occurrence of some undesirable event
• noun:   an automatic signal (usually a sound) warning of danger
• noun:   fear resulting from the awareness of danger
• noun:   a clock that wakes sleeper at preset time
• verb:   warn or arouse to a sense of danger or call to a state of preparedness

  Example: "The empty house alarmed him"

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