alarm

Noun

• a clock that wakes a sleeper at some preset time

• an automatic signal (usually a sound) warning of danger

• a device that signals the occurrence of some undesirable event

• 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
    
  • We alerted the new neighbors to the high rate of burglaries
    

• 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
    

Related words

• Synonyms: 
  alarm clock , alert , warning signal , alarum , warning device , alarm system , dismay , consternation , appal , appall , horrify