Wordnet 3.0
NOUN (2)
1. 
 a loud warning signal produced by a burglar alarm; 
- Example: "they could hear the burglar alarm a mile away"2. 
 a warning device that is tripped off by the occurrence of a burglary; 
The Collaborative International Dictionary of English v.0.48:
Burglar \Bur"glar\, n. [OE. burg town, F. bourg, fr. LL. burgus
   (of German origin) + OF. lere thief, fr. L. latro. See
   Borough, and Larceny.] (Law)
   One guilty of the crime of burglary.
   [1913 Webster]
   Burglar alarm, a device for giving alarm if a door or
      window is opened from without.
      [1913 Webster]
WordNet (r) 3.0 (2006):
burglar alarm
    n 1: a loud warning signal produced by a burglar alarm; "they
         could hear the burglar alarm a mile away"
    2: a warning device that is tripped off by the occurrence of a
       burglary