Buzzer

Etymology
to buzz + -er

Noun

 * 1) A device that makes a buzzing sound.
 * If you think you know the answer to the question, hit the buzzer as fast as you can.
 * 1) Anything that buzzes, such as an insect.
 * 2) 🇺🇸 A police badge.
 * 1) 🇺🇸 A police badge.

Thesaurus
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