A Cookie is the name given to the digitally replicated consciousness of a human being. Originally appearing in White Christmas, they have been mentioned in several other episodes.
The legal status of cookies has been shown to vary in different episodes of the series. In White Christmas, it is shown that any criminal confession from a cookie is regarded as the same as if the individual it was taken from had confessed. This is the case with Joe Potter, who has his consciousness replicated by the police and then exposed to Matt Trent, who is able to get him to confess to his crimes in 70 minutes.
However, in Black Museum it is revealed that the United Nations has implemented stricter controls on digitally replicating consciousness, stating that a cookie must be able to show at least 5 emotions for its existence to be considered "humane". It is also illegal to delete the replicated consciousness.
A device is inserted under the clients head by the brain and kept there for a week, giving it time to accurately replicate the individuals consciousness. It is then removed and installed in a larger, egg shaped device which can be connected to a computer or tablet.
Greta has her consciousness replicated through the Smartelligence service in order to have the cookie run her automated smart house. However, the replicated consciousness believes itself to be the real Greta and refuses to work, causing Matt Trent to subject it to psychological torture via increased time perception in order to break it and get it to comply.
After Joe Potter accidentally kills Gordon Grey in a fit of rage, the police arrest and interrogate him, but are unable to get him to talk. Detective's Holder and Fenn, and Home Office representative Gainsborough then decide to extract a cookie from him, and have it interact digitally with a now incarcerated Matt Trent to try and obtain a confession. Before entering the digital recreation, Trent alters the time perception, causing Joe's cookie to believe it has known him for five years. After a considerable amount of talking and coaxing, Trent is able to get a full confession from Potter in less than 70 minutes, much to the shock and delight of the police officers. Holder then informs the real Joe that his cookie has confessed, so he can keep up the silent routine as long as he wants.
Prior to clocking off for the evening over the Christmas period, Fenn asks whether they should deactivate the cookie. Holder replies that they should leave him on for Christmas. Fenn then increases the time settings to 1000 years a minute, leaving Joes cookie to be tortured to the song I Wish It Could Be Christmas Everyday on the radio. No matter how many times he smashes the radio, it returns the moment he looks back, and playing increasingly louder. He curls up on the floor, screaming.
Shut Up and Dance
Hated in the Nation
In the second story, a woman named Carrie dies, and her consciousness is placed into part of Jack's (her husband)'s brain, so she can experience his physical sensations and communicate with him. Jack and Carrie become aggravated by their lack of privacy and agency, respectively. Jack uses the "pause" feature to stop Carrie from experiencing anything. After months, he feels guilty and unpauses her. Several weeks later they agree for her to be unpaused on weekends only. Jack begins dating Emily, who wants Carrie to be deleted. Rolo transfers Carrie's cookie into a toy monkey, which can feel sensations and say two phrases, and gives the monkey to Carrie and Jack's son, Parker. Parker is quickly bored by it. When the monkey technology was deemed illegal, Rolo is fired and takes Carrie with him and displays it in his Black Museum.
Rachel, Jack and Ashley Too
Pop superstar Ashley O announces the release of the Ashley Too dolls, which are little robots capable of interacting with their users and carry full conversations. As it turns out, every Ashley Too features cookies based on the real Ashley O, which enables them to respond as Ashley herself and fully interact with their users and their environments, as well as show a degree of self-awareness, which causes nearly every Ashley Too to malfunction and freeze when they learn the real Ashley has fallen into an irreversible coma.
As the news of Ashley's months-long coma (and the recall of the Ashley Toos due to what's perceived as battery malfunctions) are accidentally heard by teenage fan Rachel Goggins' Ashley Too, it also malfunctions. Rachel and her sister Jack manage to scan the unit's "brain", using their father's equipment for studying mice, and discover a limiter that keeps the doll obedient, and its functionality based only on the portion of Ashley's brain that holds her public persona. After said lock is disengaged, the full brain becomes active and the doll starts back up with Ashley's full personality, including her moodiness and abrasiveness, all her memories, and the knowledge that the reasons given for the real Ashley's coma (a bad reaction to seafood) are a lie.
As opposed to previously shown models of cookies, where the personality is fully copied and conditioned through torture into becoming an obedient servant, Ashley's personality is merely kept into a state of servitude by a limiter that keeps it fully responsive within programmed parameters, akin to a lobotomy. As Rachel's doll is released from it, her Ashley Too shows no sign of conditioning and is fully herself (although she is aware of the limiter and glad to be released from it, which suggests a minor degree of consciousness while in such state)