Eye-5

The Eye-5 (or I-5) was a special kind of contact lenses that could be used to record the things it saw.

Functions
The Eye-5, though it looked and functioned just like a normal contact lens, could transmit information wirelessly back to a computer network. (TW: Reset) It could also be routed to all wireless networks in the area. (TW: End of the Road) Information transmitted from the lens could be recorded like conventional video. (TW: Children of Earth: Day Three) A person at the other end could then communicate with the wearer via a keyboard. (TW: Reset)

The lens could not transmit sound. (TW: Reset) To get around this, the lens had lip-reading software, which worked best when the person in question faced the camera directly. The lip-reading software translated lip movements to speech after a delay of a second or two. (TW: Children of Earth: Day Three)

The Eye-5 had several other features. It could be used to get past an iris scan by creating the image of a iris. (TW: Escape to LA) It could also be linked to detect the wearer's heartbeat, activating at a certain rate. (TW: End of the Road)

History of use
According to Jack Harkness, the Eye-5 originally came from a distant moon in a distant galaxy. (TW: Dead of Night) Torchwood Three was able to obtain a set and used it for espionage. Ianto Jones and Gwen Cooper were also known to have borrowed them for "fun". (TW: Children of Earth: Day Three)

The lenses were used by Martha Jones when infiltrating the Pharm. (TW: Reset)

Though Torchwood Three was destroyed, the Eye-5 survived due to Gwen Cooper having borrowed them. Lois Habiba used them to record secret negotiations between the British government and the 456. (TW: Children of Earth: Day Three) Downloaded onto a laptop, Rhys Williams held onto the information so that he could reveal the negotiations to the public. (TW: Children of Earth: Day Four) After the conclusion of the 456 crisis, Bridget Spears wore the lens to record Prime Minister Brian Green casually mentioning his complicity in the affair. (TW: Children of Earth: Day Five)

Gwen Cooper used the Eye-5s in 2011 to record things while infiltrating PhiCorp. (TW: Dead of Night) She also used it to get past an iris scanner at the PhiCorp headquarters. (TW: Escape to LA) When Gwen returned to Wales, she used them to record the truth of what was happening in the overflow camps. When she arrived in America, she received a text message in the lenses informing her that her mother, husband and daughter had been kidnapped, and would not be returned unless she gave them Jack. (TW: The Middle Men) Olivia Colasanto gave Gwen further instructions on the Eye-5s. (TW: Immortal Sins) After Jack and Gwen were saved, Rex Matheson stole the Eye-5s and had them activate when his heart rate increased. When he was being interrogated by Brian Friedkin, the Eye-5s recorded him, revealing Brian's acts and his betrayal of the CIA. (TW: End of the Road)

Eleventh Doctor used similar technology which allowed him to see through someone else's eyes. But whereas the Eye-5 was in the form of contact lenses, this technology was a pair of glasses. The Doctor could observe what the wearer saw via a screen in his TARDIS. (DW: The Girl Who Waited)