The primary function of the CTU key card was to allow the user inside CTU buildings; however, the cards could also store large amounts of data and could therefore be used for other things. The key card has changed appearances and uses over the course of 24. Some of the newer key cards also feature a photograph used to identify the holder.

Day 1

CTU Security Systems Analyst Scott Baylor secretly met CTU District Manager Richard Walsh at 2350 Dunlop Plaza and gave him one of the key cards that he had analyzed at Walsh's request. Baylor revealed that the magnetic strip on the card, which could hold a ton of data, contained a file with references to Senator David Palmer. He explained that the hidden file on the key card allowed the user to smuggle confidential information in and out of restricted areas. Walsh knew that the CTU agent who formatted the card was a dirty agent and was part of the plot to kill Senator Palmer.

Baylor was killed moments after handing the key card over to Walsh. Walsh contacted Jack Bauer, who arrived to help him escape. As they headed for Jack's car, a sniper shot Walsh, who tossed Jack the key card and instructed him to give it to Jamey Farrell to identify the owner and dirty agent.

Jack scanned the card and sent the information to Jamey, who identified the electronic signature. The card belonged to Nina Myers. Nina, however, was cleared of suspicion when Jamey discovered the card had been programmed on January 14th, when she and Jack had been in Santa Barbara. The card was most likely programmed by Jamey herself, using Nina's computer during her absence to point suspicion at her.

Assassin Ira Gaines compromised Jack at St. Marks Hospital and eventually ordered him to enter CTU and switch the card where freelancer Milo Pressman was trying to decrypt it and find a name for the shooter aiming for the target, David Palmer. Jack caused a diversion and switched the card with a forged one Ira placed in a car. Milo and Nina Myers discovered Jack made the switch and she confronted him, which led to her supposed death, which Jack staged using a flak jacket. The key card was later forgotten when the attempt on Palmer's life failed.

The Game

• Chase Found Out: CTU Agent Chase Edmunds used two different key cards in order to lock down the Carr's terrorist base in Washington D.C.

• Kim Goes Back In: With help from CTU Agent Tony Almeida, CTU recruit Kim Bauer gained a key card from Tony's office in order to get into the Data Room and get CTU's hard drive.

• Through the Agency: CTU Agent Jack Bauer entered CTU Los Angeles Agency Headquarters pretending to be a part of a tour inside. Peter Madsen has Jack get decrypting software inside, which required Jack to steal a key card to gain access to the restricted part of the building.

• Chase Infiltrates the Tech Lab: Chase Edmunds, undercover, infiltrated the NJH Science Technology building. In order to get inside, he needed a key card. He got one after he told the secretary there that he had an appointment Doctor Phillips. When the secretary went to check the log, he stole the key card that was on the desk.

• Accessing The Computer Labs: Chase Edmunds helped Jack Bauer retrieve the CTU hard drive, which was at Joseph Sin-Chung's base. In order to do so, Chase followed and incapacitated one of Joseph's men, stealing his key card and giving it to Jack so he could enter the computer lab and retrieve the CTU hard drive.

• Looking for Kate: Jack Bauer took key card off a killed terrorist and used it to open Kate Warner's cell.

• Searching Radford's Office: Tony Almeida gained access to Governor James Radford's office with the use of a key card given to him by Kathy Weis.

Day 5

• "9:00am-10:00am": At President Logan's Hidden Valley retreat, Martha Logan demanded the key card of communications office worker Burke, threatening to cry rape if he didn't hand it over. She used the card to enter the archive room and locate the transcript of her call with David Palmer, the only proof that she was not imagining it. After finding the transcript, she slipped the card back into Burke's shirt pocket.

• "10:00am-11:00am": At Ontario Airport, a terrorist, Achmed, found the key card that Chevensky hid, and reported it to Anton Beresch's lieutenant. The lieutenant delivered it to Anton Beresch, who then passed it on to Ivan Erwich. At the end of the hour, Erwich used it to open the sealed transport crate containing 20 canisters of Sentox VX nerve gas.

• "1:00pm-2:00pm": Jenny McGill arranged a meeting with her brother Lynn, asking him to bring her money. When he told her he hadn't brought her anything but the name of a doctor, her boyfriend, Dwayne Thompkins, mugged Lynn and stole his wallet, watch, and key card.

• "5:00pm-6:00pm": Lynn called Jenny for the second time, and again she tried to return the card, but Dwayne revealed that he had sold it for $20,000. (And he needed it to cut the remains of their cocaine stash into lines.) When the buyer, Ostroff, arrived to collect, he shot both Dwayne and Jenny in the back of the head.

• "6:00pm-7:00pm": After taking five minutes to reprogram the key card with his photograph and the name "Mark L. Marcus," Ostroff infiltrated CTU Los Angeles and released a canister of Sentox VX nerve gas into the ventilation system.

• "8:00pm-9:00pm": Miles Papazian commandeered Chloe O'Brian's key card, claiming to need it to reinstall operating protocols for everyone in her group. Later, she dumped coffee in his lap as a diversion, so that she could use the card long enough to download the top-secret WET list for Jack Bauer.

• "12:00am-1:00am": After Miles had Chloe taken into custody, she stole her card from his shirt pocket and used it to get out of the building.