signalling device
communication device for signalling
flag
distinctive image used as a symbol, traditionally embodied as a piece of fabric
pinger
acoustic signal device
starting pistol
acoustic signal generator to launch sports competitions
factory whistle
steam whistle used to signal beginning of work shift or an emergency
speaking horn
passive cone-shaped voice amplifier
doorbell
signaling device placed near an entry door to a building
emergency vehicle equipment
audio and visual warning signs on emergency vehicles