alarm in WordNet English dictionary

1. a device that signals the occurrence of some undesirable event
   alarm  warning device  alarm system 
   
2. a clock that wakes a sleeper at some preset time
   alarm clock  alarm 
   
3. an automatic signal (usually a sound) warning of danger
   alarm  alert  warning signal  alarum 
   
4. fear resulting from the awareness of danger
   alarm  dismay  consternation 
   

1. 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"
   alarm  alert 
   
2. 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"
   dismay  alarm  appal  appall  horrify