Eye-5

The Eye-5 (or I-5) was a special kind of contact lens 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 info wirelessly back to a computer network. (TV: Reset) It could also be routed to all wireless networks in the area and could even broadcast on TVs. (TV: End of the Road) Information transmitted from the lens could be recorded like conventional video. (TV: Children of Earth: Day Three) A person at the other end could communicate with the wearer via a keyboard. (TV: Reset)

The lens could not transmit sound. (TV: 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. (TV: Children of Earth: Day Three) However, the lenses were seemingly upgraded as when Rex Matheson used them, they could transmit audio. (TV: End of the Road)

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

History of use
According to Jack Harkness, the Eye-5 originally came from a distant moon in a distant galaxy. (TV: 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" that is implied to have been of a sexual nature. (TV: Children of Earth: Day Three)

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

Though Torchwood Three was destroyed, the Eye-5 survived due to Gwen Cooper having borrowed them for "fun" with Rhys Williams. Though the team possessed limited resources, the Eye-5 software still existed on the Torchwood server and Ianto downloaded it to a laptop at Gwen's request. Lois Habiba used them to record secret negotiations between the British government and the 456. (TV: 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. (TV: 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. (TV: Children of Earth: Day Five)

Gwen Cooper used the Eye-5s in 2011 to record while infiltrating PhiCorp. (TV: Dead of Night) She also used it to get past an iris scanner at the PhiCorp headquarters. (TV: Escape to LA) When Gwen returned to Wales, she used them to record 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. (TV: The Middle Men) Olivia Colasanto gave Gwen further instructions on the Eye-5s and Rex Matheson and Esther Drummond found and rescued her and Jack by tracking the Eye-5's after hacking in when they got suspicious. (TV: Immortal Sins) After Jack and Gwen were saved, Rex 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. (TV: End of the Road)