A key card was an object to open an electronic lock.
After being caught by the Deputy Chief Caretaker, the Seventh Doctor was able to trick him so he could escape. As he left, he took the Deputy's key card. (TV: Paradise Towers)
The Eleventh Doctor used Gol Clutha's key card to explore the ship. (COMIC: Hunters of the Burning Stone)
Bernice Summerfield stole Bernard Moskof's key card, copied it, then carefully put it back in his pocket. (PROSE: Drinking with the Enemy)
Darius Pike stole a key card from prison governor Thorne and gave it to Jorjie Turner. (TV: Liberation)