A doorbell is a signaling device typically placed near a
door
A door is a hinged or otherwise movable barrier that allows ingress (entry) into and egress (exit) from an enclosure. The created opening in the wall is a ''doorway'' or ''portal''. A door's essential and primary purpose is to provide securit ...
to a building's entrance. When a visitor presses a
button
A button is a fastener that joins two pieces of fabric together by slipping through a loop or by sliding through a buttonhole.
In modern clothing and fashion design, buttons are commonly made of plastic but also may be made of metal, wood, or ...
, the
bell
A bell /ˈbɛl/ () is a directly struck idiophone percussion instrument. Most bells have the shape of a hollow cup that when struck vibrates in a single strong strike tone, with its sides forming an efficient resonator. The strike may be m ...
rings inside the building, alerting the occupant to the presence of the visitor. Although the first doorbells were mechanical, activated by pulling a cord connected to a bell, modern doorbells are electric, operated by a pushbutton switch. Modern doorbells often incorporate
intercom
An intercom, also called an intercommunication device, intercommunicator, or interphone, is a stand-alone voice communications system for use within a building, small collection of buildings or portably within a small coverage area, which funct ...
s and miniature
video camera
A video camera is an optical instrument that captures videos, as opposed to a movie camera, which records images on film. Video cameras were initially developed for the television industry but have since become widely used for a variety of other ...
s to increase security.
History
William Murdoch
William Murdoch (sometimes spelled Murdock) (21 August 1754 – 15 November 1839) was a Scottish chemist, inventor, and mechanical engineer.
Murdoch was employed by the firm of Boulton & Watt and worked for them in Cornwall, as a steam engin ...
, a Scottish inventor, installed a number of his own innovations in his house, built in
Birmingham
Birmingham ( ) is a City status in the United Kingdom, city and metropolitan borough in the metropolitan county of West Midlands (county), West Midlands, within the wider West Midlands (region), West Midlands region, in England. It is the Lis ...
in 1817; one of these was a loud doorbell, that worked using a piped system of compressed air. A precursor to the electric doorbell, specifically a bell that could be rung at a distance via an electric wire, was invented by
Joseph Henry
Joseph Henry (December 17, 1797– May 13, 1878) was an American physicist and inventor who served as the first secretary of the Smithsonian Institution. He was the secretary for the National Institute for the Promotion of Science, a precursor ...
around 1831. By the early 1900s, electric doorbells had become commonplace.
Wired doorbells
In most wired systems, a button on the outside next to the door, located around the height of the doorknob, activates a signaling device (usually a
chime,
bell
A bell /ˈbɛl/ () is a directly struck idiophone percussion instrument. Most bells have the shape of a hollow cup that when struck vibrates in a single strong strike tone, with its sides forming an efficient resonator. The strike may be m ...
, or
buzzer
A buzzer or beeper is an audio signaling device, which may be mechanical, electromechanical, or piezoelectric (''piezo'' for short). Typical uses of buzzers and beepers include alarm devices, timers, train and confirmation of user input such ...
) inside the building. Pressing the doorbell button, a single-pole, single-throw (SPST) pushbutton
switch
In electrical engineering, a switch is an electrical component that can disconnect or connect the conducting path in an electrical circuit, interrupting the electric current or diverting it from one conductor to another. The most common type o ...
momentarily closes the doorbell circuit. One
terminal of this button is wired to a terminal on a
transformer
In electrical engineering, a transformer is a passive component that transfers electrical energy from one electrical circuit to another circuit, or multiple Electrical network, circuits. A varying current in any coil of the transformer produces ...
. A doorbell transformer steps down the 120 or 240-volt
AC electrical power to a lower
voltage
Voltage, also known as (electrical) potential difference, electric pressure, or electric tension, is the difference in electric potential between two points. In a Electrostatics, static electric field, it corresponds to the Work (electrical), ...
, typically 6 to 24 volts. The transformer's other terminal connects to one of three terminals on the signaling device. Another terminal is connected to a wire that travels to the other terminal on the button. Some signaling devices have a third terminal, which produces a different sound. If there is another doorbell button (typically near a back door), it is connected between the transformer and the third terminal. The transformer
primary winding, being energized continuously, does consume a small amount (about 1 to 2 watts) of
standby power
Standby power, also called vampire power, vampire draw, phantom load, ghost load, or leaking electricity, refers to how certain electronic and electrical appliances consume electricity while they are not actively in use, but which are still ...
constantly; systems with lighted pushbutton switches may consume a similar amount of power per switch. The tradeoff is that the wiring to the button carries only safe, low-voltage power isolated from
earth ground.
A common signaling device is a chime unit consisting of two flat metal bar resonators, which are struck by a plunger operated by a
solenoid
upright=1.20, An illustration of a solenoid
upright=1.20, Magnetic field created by a seven-loop solenoid (cross-sectional view) described using field lines
A solenoid () is a type of electromagnet formed by a helix, helical coil of wire whos ...
. The flat bars are tuned to two pleasing notes. When the doorbell button is pressed, the solenoid's plunger strikes one bar, and when the button is released, a
spring on the plunger pushes the plunger back, causing it to strike the other bar, creating a two-tone sound ("''ding-dong''"). If a second doorbell button is used, it might be wired to a second solenoid, which strikes only one of the bars, to create a single-tone sound ("''ding''"). Alternatively, the second button might feed the single solenoid via an oscillating switch (often a
mercury tilt switch), to give a "warbling" sound ("''ding-dong-ding-dong-ding-dong''"). The Edwards Sylvan C-26 had both additional features, suiting three doors. Some chimes have
tubular bells
Tubular bells (also known as chimes) are musical instruments in the Percussion instrument, percussion family. Their sound resembles that of church bells, carillons, or a bell tower; the original tubular bells were made to duplicate the soun ...
instead of bars.
More elaborate doorbell chimes play a short musical tune, such as the
Westminster Quarters.
Doorbells for
hearing-impaired people use visual signaling devices — typically
light bulb
Electric light is an artificial light source powered by electricity.
Electric Light may also refer to:
* Light fixture, a decorative enclosure for an electric light source
* ''Electric Light'' (album), a 2018 album by James Bay
* Electric Light ( ...
s — rather than audible signaling devices.
Fully battery-powered wired models are also common, either using a two-bar design or an electric bell. These do not consume standby power, but require the user to change the batteries, which are usually large primary cells located in the
bell box
A bell box is an audible device, often Electricity, electric, which when activated, emits a Warning chime, chime, bell, or buzzer sound.
Components
The housing of the bell box may be manufactured from wood, metal, or plastic. The basic core comp ...
.
Wireless doorbells

In recent decades, wireless doorbells have become popular, to avoid the expense of running wires through the building walls. The doorbell button contains a built-in
radio transmitter
In electronics and telecommunications, a radio transmitter or just transmitter (often abbreviated as XMTR or TX in technical documents) is an electronic device which produces radio waves with an antenna with the purpose of signal transmissio ...
powered by a battery. When the button is pushed, the transmitter sends a
radio
Radio is the technology of communicating using radio waves. Radio waves are electromagnetic waves of frequency between 3 hertz (Hz) and 300 gigahertz (GHz). They are generated by an electronic device called a transmitter connec ...
signal to the receiver unit, which is plugged into a wall outlet inside the building. When the radio signal is detected by the
receiver, it activates a sound chip that plays the sound of gongs through a
loudspeaker
A loudspeaker (commonly referred to as a speaker or, more fully, a speaker system) is a combination of one or more speaker drivers, an enclosure, and electrical connections (possibly including a crossover network). The speaker driver is an ...
—either a two-note "ding-dong" sound, or a longer chime sequence such as the ''
Westminster Quarters''.
Frequencies
Frequency is the number of occurrences of a repeating event per unit of time. Frequency is an important parameter used in science and engineering to specify the rate of oscillatory and vibratory phenomena, such as mechanical vibrations, audio ...
in the 2.4 GHz
ISM band
The ISM radio bands are portions of the radio spectrum reserved internationally for ''industrial, scientific, and medical'' (ISM) purposes, excluding applications in telecommunications.
Examples of applications for the use of radio frequency (RF ...
are usually used. To avoid interference by nearby wireless doorbells on the same radio
frequency
Frequency is the number of occurrences of a repeating event per unit of time. Frequency is an important parameter used in science and engineering to specify the rate of oscillatory and vibratory phenomena, such as mechanical vibrations, audio ...
, the units can usually be set by the owner to different radio channels.
In larger metropolitan cities, a trend has developed over the past decade that uses telephone technology to wirelessly signal doorbells, as well as to answer the doors and remotely release
electric strike
An electric strike is an access control device used for door frames. It replaces the fixed strike faceplate often used with a latch (also known as a ''keeper'').
Description
Like a fixed strike plate, an electric strike plate normally prese ...
s. In many cities throughout the world, this is the predominant form of doorbell signalling.
Musical and continuous power doorbells
As with wireless doorbells, musical doorbells have also become more common. Musical and continuous power doorbells serve as an attempt to bridge the gap between newer digital circuitry and older doorbell wiring schemes. A major difference between the standard setup of a wired doorbell and a musical doorbell is that the musical doorbell must maintain power after the doorbell button is released, to continue playing the doorbell song. This can be achieved in one of two ways.
For simple
single-pole, single-throw doorbell buttons, the chime device employs a
rectifier
A rectifier is an electrical device that converts alternating current (AC), which periodically reverses direction, to direct current (DC), which flows in only one direction.
The process is known as ''rectification'', since it "straightens" t ...
diode and ballast capacitor at the voltage input stage of the circuit. Upon pressing the doorbell button, power is connected through the rectifier diode or series of rectifier diodes called a full wave rectifier, which allows the current to flow in only one direction, into the ballast capacitor. The ballast capacitor charges at a rate far greater than the rest of the circuit needs to complete a given song. Once the button is released, the capacitor retains the charge and maintains power for a short duration to the rest of the circuit.
For mixed wireless and wired input doorbells, a special doorbell button is needed to maintain power continuously to the doorbell chime. The circuit is similar to the one above, except that the rectifier diode is now moved into the doorbell button housing. Pressing the doorbell button allows both negative and positive sides of the AC power signal to flow into the circuit, while releasing the button only allows either the positive or negative side to flow into the circuit. By differentiating the full and half wave signals, the doorbell is able to function as it does in the previous wired case, while also providing continuous power to the doorbell for other purposes, such as receiving wireless doorbell button input.
Smart doorbells
With the rise of the
Internet of Things
Internet of things (IoT) describes devices with sensors, processing ability, software and other technologies that connect and exchange data with other devices and systems over the Internet or other communication networks. The IoT encompasse ...
in the 2010s, a number of internet-connected bell systems, known as
smart doorbell
A smart doorbell is an internet-connected doorbell that notifies the home owner on their device (smartphone or any other gadget) when a visitor arrives at the door. It activates when the visitor presses the button of the doorbell, or alternativel ...
s have appeared on the market.
Popular systems include the
Ring
(The) Ring(s) may refer to:
* Ring (jewellery), a round band, usually made of metal, worn as ornamental jewelry
* To make a sound with a bell, and the sound made by a bell
Arts, entertainment, and media Film and TV
* ''The Ring'' (franchise), a ...
doorbell,
Vivint
Vivint Smart Home, Inc. is a Provo, Utah-based manufacturer of smart home and home security products. Its product lines include cameras, locks, safety sensors, thermostats, and lighting, along with associated monitoring and installation services. ...
Home Security doorbell, and the
Nest Hello. These consist of a single unit which is located in place of the traditional push-button, and in addition to a physical button, contains a high-definition camera,
passive infrared sensor
A passive infrared sensor (PIR sensor) is an electronic sensor that measures infrared (IR) light radiating from objects in its field of view. They are most often used in PIR-based motion detectors. PIR sensors are commonly used in security alarms ...
and Wi-Fi capability. The device is connected to the home Wi-Fi network, and notifications of a button-press or detected movement are pushed to a paired
smartphone
A smartphone is a mobile phone with advanced computing capabilities. It typically has a touchscreen interface, allowing users to access a wide range of applications and services, such as web browsing, email, and social media, as well as multi ...
or other electronic device such as a
tablet. When a notification is received, the user will typically see a live video stream from the smart doorbell, showing who is at the door and potentially allowing a 2-way audio conversation.
The devices can be powered by an internal battery, or they may use the existing bell wiring for continuous power.
The video is typically recorded via Wi-Fi to a
cloud internet service, meaning that if the unit is tampered with, damaged or stolen, then this recording will still be captured and can be analyzed to determine the identity of the responsible party.
See also
*
Bell pull
*
Call bell – a counter top bell used to call attention of the staff at a service desk
*
Door knocker
*
Intercom
An intercom, also called an intercommunication device, intercommunicator, or interphone, is a stand-alone voice communications system for use within a building, small collection of buildings or portably within a small coverage area, which funct ...
References
External links
{{Authority control
Bells (percussion)
Bell
A bell /ˈbɛl/ () is a directly struck idiophone percussion instrument. Most bells have the shape of a hollow cup that when struck vibrates in a single strong strike tone, with its sides forming an efficient resonator. The strike may be m ...
1831 introductions