A buzzer or beeper is a signalling device, usually
electronic, typically used in automobiles, household appliances
such as a microwave oven, or game shows.
It most commonly consists of a number of switches or sensors connected
to a control unit that determines if and which button was pushed
or a preset time has lapsed, and usually illuminates a light on
the appropriate button or control panel, and sounds a warning in
the form of a continuous or intermittent buzzing or beeping sound.
Initially this device was based on an electromechanical system which
was identical to an electric bell without the metal gong (which
makes the ringing noise). Often these units were anchored to a wall
or ceiling and used the ceiling or wall as a sounding board. Another
implementation with some AC-connected devices was to implement a
circuit to make the AC current into a noise loud enough to drive
a loudspeaker and hook this circuit up to a cheap 8-ohm speaker.
Nowadays, it is more popular to use a ceramic-based piezoelectric
sounder like a Sonalert which makes a high-pitched tone. Usually
these were hooked up to "driver" circuits which varied
the pitch of the sound or pulsed the sound on and off.
In game shows it is also known as a "lockout system,"
because when one person signals ("buzzes in"), all others
are locked out from signalling. Several game shows have large buzzer
buttons which are identified as "plungers".
The word "buzzer" comes from the rasping noise that buzzers
made when they were electromechanical devices, operated from stepped-down
AC line voltage at 50 or 60 cycles. 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,
instead using light.