The Collaborative International Dictionary of English v.0.48:

Buzzer \Buzz"er\ (b[u^]z"[~e]r), n.
   One who, or that which, buzzes; a whisperer; a talebearer.
   [1913 Webster]

         And wants not buzzers to infect his ear
         With pestilent speeches of his father's death. --Shak.
   [1913 Webster]

WordNet (r) 3.0 (2006):

buzzer
    n 1: a push button at an outer door that gives a ringing or
         buzzing signal when pushed [syn: doorbell, bell,
         buzzer]
    2: a signaling device that makes a buzzing sound

Moby Thesaurus II by Grady Ward, 1.0:

44 Moby Thesaurus words for "buzzer":
   Klaxon, Mayday, SOS, air-raid alarm, alarm, alarm bell,
   alarm clock, alarm signal, alarum, alert, all clear, beacon,
   blinking light, burglar alarm, crostarie, fiery cross, fire alarm,
   fire bell, fire flag, five-minute gun, flashing light, fog bell,
   fog signal, foghorn, gale warning, hooter, horn, hue and cry,
   hurricane warning, lighthouse, note of alarm, occulting light,
   police whistle, signal of distress, siren, small-craft warning,
   still alarm, storm cone, storm flag, storm warning, tocsin,
   two-minute gun, upside-down flag, whistle