A straight key style of telegraph key – model J-38, a key used by U.S. military during World War II, and frequently re-used by radio amateurs
Chart of the Morse code 26 letters and 10 numerals
Cooke and Wheatstone's five-needle telegraph from 1837
a Wright Brothers telegraph key (missing its knob)
This Morse key was originally used by Gotthard railway, later by a shortwave radio amateur
Morse Telegraph
A Morse Key from G. Hasler, Bern (1900)
Single needle telegraph instrument
Hughes telegraph, an early (1855) teleprinter built by Siemens and Halske
Early "bug" telegraph key invented in 1913 by Weston Hadden
Telegraph key and sounder. The signal is "on" when the knob is pressed, and "off" when it is released. Length and timing of the dits and dahs are entirely controlled by the telegraphist.
Sömmering's electric telegraph in 1809
Electronic dual paddle keyer (homemade in 1972)
Morse code receiver, recording on paper tape
Revolving alphanumeric dial created by Francis Ronalds as part of his electric telegraph (1816)
Comparison of historical versions of Morse code with the current standard. Left: Later American Morse code from 1844. Center: The modified and rationalized version used by Friedrich Gerke on German railways. Right: Current ITU standard.
Pavel Schilling, an early pioneer of electrical telegraphy
A U.S. Navy Morse Code training class in 2015. The sailors will use their new skills to collect signals intelligence.
Diagram of alphabet used in a 5-needle Cooke and Wheatstone Telegraph, indicating the letter G
A commercially manufactured iambic paddle used in conjunction with an electronic keyer to generate high-speed Morse code, the timing of which is controlled by the electronic keyer.
Morse key and sounder
A U.S. Navy signalman sends Morse code signals in 2005.
GWR Cooke and Wheatstone double needle telegraph instrument
Cayo Largo Del Sur VOR-DME.
A magneto-powered Wheatstone A. B. C. telegraph with the horizontal "communicator" dial, the inclined "indicator" dial and crank handle for the magneto that generated the electrical signal.
Vibroplex brand semiautomatic key (generically called a "bug"). The paddle, when pressed to the right by the thumb, generates a series of dits, the length and timing of which are controlled by a sliding weight toward the rear of the unit. When pressed to the left by the knuckle of the index finger, the paddle generates a single dah, the length of which is controlled by the operator. Multiple dahs require multiple presses. Left-handed operators use a key built as a mirror image of this one.
Professor Morse sending the message – WHAT HATH GOD WROUGHT on 24 May 1844
Representation of Morse code.
Foy–Breguet telegraph displaying the letter "Q"
Graphical representation of the dichotomic search table. The graph branches left for each dot and right for each dash until the character representation is exhausted.
Wheatstone automated telegraph network equipment
Scout movement founder Baden-Powell's mnemonic chart from 1918
A Baudot keyboard, 1884
Phelps' Electro-motor Printing Telegraph from circa 1880, the last and most advanced telegraphy mechanism designed by George May Phelps
A Creed Model 7 teleprinter in 1930
Teletype Model 33 ASR (Automatic Send and Receive)
Major telegraph lines in 1891
The Eastern Telegraph Company network in 1901
German Lorenz SZ42 teleprinter attachment (left) and Lorenz military teleprinter (right) at The National Museum of Computing on Bletchley Park, England

A telegraph key is a specialized electrical switch used by a trained operator to transmit text messages in Morse code in a telegraphy system.

- Telegraph key

Keys are used in all forms of electrical telegraph systems, including landline (also called wire) telegraphy and "wireless" and radio (also called wireless) telegraphy.

- Telegraph key

Morse code is named after Samuel Morse, one of the inventors of the telegraph.

- Morse code

At the sending station, an operator would tap on a switch called a telegraph key, spelling out text messages in Morse code.

- Electrical telegraph

Although the traditional telegraph key (straight key) is still used by some amateurs, the use of mechanical semi-automatic keyers (known as "bugs") and of fully automatic electronic keyers is prevalent today.

- Morse code
A straight key style of telegraph key – model J-38, a key used by U.S. military during World War II, and frequently re-used by radio amateurs

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A US Army Signal Corps radio operator in 1943 in New Guinea transmitting by radiotelegraphy

Wireless telegraphy

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A US Army Signal Corps radio operator in 1943 in New Guinea transmitting by radiotelegraphy
Amateur radio operator transmitting Morse code
Tesla's explanation in the 1919 issue of "Electrical Experimenter" on how he thought his wireless system would work
Thomas Edison's 1891 patent for a ship-to-shore wireless telegraph that used electrostatic induction
Example of transatlantic radiotelegraph message recorded on paper tape at RCA's New York receiving center in 1920. The translation of the Morse code is given below the tape.
In World War I balloons were used as a quick way to raise wire antennas for military field radiotelegraph stations. Balloons at Tempelhofer Field, Germany, 1908.
Guglielmo Marconi, the father of radio-based wireless telegraphy, in 1901, with one of his first wireless transmitters (right) and receivers (left)
German troops erecting a wireless field telegraph station during World War I
German officers and troops manning a wireless field telegraph station during World War I
Mobile radio station in German South West Africa, using a hydrogen balloon to lift the antenna

Wireless telegraphy or radiotelegraphy is transmission of telegraph signals by radio waves.

In radiotelegraphy, information is transmitted by pulses of radio waves of two different lengths called "dots" and "dashes", which spell out text messages, usually in Morse code.

In a manual system, the sending operator taps on a switch called a telegraph key which turns the transmitter on and off, producing the pulses of radio waves.