Buzzer

A buzzer is an lockout signalling device, usually electronic, typically used on game shows such as Jeopardy! or at competitive events such as quizbowl. It most commonly consists of a number of buttons connected to a central unit that determines which button was pushed first and usually illuminates a light on the appropriate button.

Also known as a "lockout system," because when one person signals ("buzzes in"), all others are locked out from signalling.

The word "buzzer" presumably comes from the buzzing noise that some buzzers make. Other sounds commonly used to indicate that a button has been pressed are a ring or a beep. Some systems, such as the one used on Jeopardy!, make no noise at all, content to use only light and not sound.