(n.) An instrument for intensifying and making audible very feeble sounds. It produces its effects by the changes of intensity in an electric current, occasioned by the variations in the contact resistance of conducting bodies, especially of imperfect conductors, under the action of acoustic vibrations.

AM transmitter FM transmitter Klaxon Mayday RT transmitter Roman candle SOS Texas tower Very flare aid to navigation air-raid alarm airport beacon airway beacon alarm alarm bell alarm clock alarm signal alarum alert all clear amateur transmitter amber light anchor light approach light backfire balefire beacon fire beacons beam bell bell buoy belvedere blaze bleachers blinker blinker light blinking light blue peter bonfire bridge buoy burglar alarm burning ghat buzzer campfire caution light ceiling light cheerful fire combustion conflagration conning tower corposant cozy fire crackling fire crematory crostarie death fire fan marker fen fire fiery cross fire fire alarm fire bell fire flag five-minute gun flame flare flare path flare-up flashing light flashing point flicker flickering flame fog bell fog signal fog whistle foghorn forest fire fox fire funeral pyre fusee gale warning gallery gazebo glance go light gong buoy grandstand green light heliograph high sign hooter horn hue and cry hurricane warning ignis fatuus ignition ingle international alphabet flag international numeral pennant kick lambent flame leer light lighthouse lightship lookout loophole magnesium flare marker marker beacon marshfire microphone navigation light nod note of alarm nudge observation post observatory occulting light open fire outlook overlook parachute flare peanut gallery peephole pharos pilot flag poke police whistle prairie fire pylon pyre quarantine flag racon radar beacon radiator radio beacon radio range beacon radio transmitter radiomicrophone radiosonde raging fire red flag red light ringside ringside seat rocket sailing aid sea of flames semaphore semaphore flag semaphore telegraph sheet of fire sighthole sign signal signal beacon signal bell signal fire signal flag signal flare signal gong signal gun signal lamp signal light signal mast signal of distress signal post signal rocket signal shot signal siren signal tower siren skyrocket small-craft warning smudge fire spar buoy still alarm stop light storm cone storm flag storm warning the nod the wink three-alarm fire tocsin top gallery touch tower traffic light traffic signal transceiver transmitter two-alarm fire two-minute gun upside-down flag watch fire watchtower whistle white flag wigwag wigwag flag wildfire wind cone wind indicator wind sock wink witch fire yellow flag