Earpiece

Earpieces were wearable communication devices used on Earth. They were worn on the ear for the purpose of private communication.

Earpieces had various unique designs. Some were prominently worn on the ear, (TV: Dalek et al) while a more common earpiece design was that of a smaller, acoustic tube. (TV: Aliens of London et al) Certain earpieces were designed to be practically near invisible. (TV: Kiss Kiss, Bang Bang)

Some earpieces had microphones attached, while less conspicuous designs had them separate. (TV: Dalek, Children of Earth: Day One etc.)

Use by humans
Earpieces were often used in certain professions, such as by members of intelligence agencies, police, and private organisations. (TV: Dalek, Army of Ghosts etc.) Television and news presenters also used earpieces to receive communication from their studio. (TV: Aliens of London) In 2006, as a newsreader, Trinity Wells reported that the United Nations Security Council had voted to release the codes for nuclear weapons to the British government, after being informed of the vote's passing through an earpiece. (TV: World War Three)

The Torchwood Institute had their own issued earpieces for personnel. (TV: Army of Ghosts, Everything Changes etc.) The Unified Intelligence Taskforce also provided earpieces for its officers by the 21st century. (TV: The Sontaran Stratagem) While working at UNIT's headquarters in New York, Martha Jones used an earpiece to keep in contact with Jack Harkness during the 2009 Dalek invasion of Earth. (TV: The Stolen Earth)

Earpieces could be damaged by sonic devices. When cornered at Combat 3000, Sarah Jane Smith used her sonic lipstick on Mark Grantham's earpiece, which caused electricity and loud feedback to emit from it, allowing Sarah Jane to escape. (TV: Warriors of Kudlak) She would later do the same to the earpieces of a group of UNIT guards at the Black Archive. (TV: Enemy of the Bane)

When pursuing the Torchwood Three team, Agent Johnson constantly wore a tube earpiece. Through it, she was able to communicate with her base of operations. (TV: Children of Earth: Day One et al)

K9 Mark IV had the ability to relay his voice into an earpiece. Clyde Langer used this in order to cheat at an exam. (TV: The Gift)

In 2012, Diana Goddard often wore an earpiece while working at GeoComTex. She used this earpiece to communicate with other staff, such as Danny Simmons. The security officers at the Vault also had earpieces. (TV: Dalek)

In 2040, the Personal Associative Network ID system functioned as a communications device and entertainment system. It had attachable earpieces and microphones. (PROSE: /Carpenter/Butterfly/Baronet)

The crewmembers of the Drum had earpiece communicators. (TV: Before the Flood)

Use by the Doctor
In situations that required them to remain in contact with the TARDIS, the Doctor has used an earpiece. On three occasions, the Eleventh Doctor used an earpiece for this purpose. On the first of these occasions, the Doctor used an advanced earpiece to remain in contact with Amy Pond in the TARDIS, who was stuck in the time vortex due to interference from 79B Aickman Road. The Doctor was stuck in Colchester, and in an attempt to remain hidden while investigating the flat, used an earpiece which "scrambled" his speech and made it sound like gibberish to anybody else listening. (TV: The Lodger) The Doctor would once again use an earpiece to communicate with Amy while stuck outside the TARDIS, this time due to a "space riptide". (GAME: TARDIS) The Doctor would also use an earpiece to remain in contact with "Handles" while teleporting to other ships, giving instructions to Handles who controlled the TARDIS teleportation system. (TV: The Time of the Doctor)

This situation also happened in reverse, when the Doctor needed to remain in contact with an individual from inside the TARDIS. This was the case for the Twelfth Doctor, who gave Clara Oswald an earpiece while he was trapped inside the TARDIS as its external shell had been reduced in size. This earpiece used nanotechnology which hacked into Clara's optic nerve when placed in her ear, allowing the Doctor to see from her point of view with the TARDIS scanner. (TV: Flatline) While testing Missy's "goodness", the Twelfth Doctor allowed her to take his place in answering a distress call, instructing her from an earpiece from the TARDIS. Bill Potts and Nardole acted as her "companions", and also wore the same earpieces. (TV: World Enough and Time)

Use by the Cybermen
The Cybermen frequently used earpieces as a means of controlling humans. This was especially common with the Cybermen of Pete's World, who captured individual humans and coverted them into Cyber-agents using modified earpieces to control them with Cyber-filament connecting them to the human brain. (TV: Army of Ghosts)

After escaping the Void, the Cybermen found themselves in London in 1851. They once again used earpieces, this time cruder versions to control workhouse owners. They allowed a human ally, Mercy Hartigan, control over the earpieces. Once the controlled workhouse owners had fulfilled their purpose of bringing their children to the CyberKing, Miss Hartigan disposed of them by pulling a lever which electrified the earpieces, killing them. (TV: The Next Doctor)

Use by other species
Earpiece-like devices were also used on other planets and among different species. The Tritovore trading ship that crashed on San Helios had earpiece internal communication devices. These earpieces fit human ears perfectly, and were used by the Tenth Doctor and Christina de Souza while trying to retrieve the ship's crystal power source. (TV: Planet of the Dead)

While posing as a human, Mrs Wormwood used an earpiece to communicate with the Bane staff at the Bubble Shock! factory. (TV: Invasion of the Bane)

Other realities
In Pete's World, earpieces called EarPods were in common use by the residents of the parallel world. They were produced by Cybus Industries, and were more technologically advanced than the earpieces of the Doctor's universe's Earth. As well as communication, the EarPods also allowed their wearers to download information into their brains as well as serving as covert mind control devices. (TV: Rise of the Cybermen, The Age of Steel), (PROSE: EarPod)