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A TARDIS key was the key to the exterior door of a TARDIS. They could be found in a variety of shapes and designs. Whatever the key’s shape and size, and whatever form the TARDIS’ outer plasmic shell, the key would fit a lock somewhere in the structure. The Doctor’s TARDIS key could be used to open TARDISes other than his own. (The Mark of the Rani)
The key could remotely lock the TARDIS from a distance, similar to some car keys. (The End of Time)The Doctor usually had his TARDIS key on his person at any given time. There were numerous other known copies of his key.A spare key was made by the First Doctor to replace one Marco Polo had taken away. Marco took away the spare as well and later returned both. (Marco Polo)
The Chancellery Guard on Gallifrey had cypher indent keys, which were TARDIS master keys of varying shapes under the control of the Castellan’s office. Some of these worked by being inserted into the keyhole, some worked by simply being held near the lock. (The Deadly Assassin, The Invasion Of Time).
When Sarah Jane Smith left the key in the lock without opening the door, it cancelled the pause control. The TARDIS travelled to its set coordinates on Earth, instead of remaining in the copy of Devesham created by the Kraal. (The Android Invasion).
A spare copy of the spade-type key kept by the Seventh and Eighth Doctors was stored in a secret compartment in the TARDIS’ outer shell. It was used by the Eighth Doctor when Chang Lee had stolen the original from his possessions. (The TV Movie)
When the TARDIS fell through a wound in time, The Doctor realised he could use the key – still warm and in contact with the ship – to bring it back. (Father’s Day)If modified properly, the TARDIS keys exhibited perception filter properties similar to that of the TARDIS. (The Sound of Drums)The Claw Shansheeth attempted to conjure a copy of The Doctor’s TARDIS key through use of a memory weave on Sarah Jane and Jo Jones’ minds. Sarah Jane and Jo overloaded the device and the partially created key disappeared. (Death of the Doctor)
Clara Oswin Oswald received a copy of the key, although she lost it when the ice sculpture governess pulled her out of the TARDIS. However, The Doctor returned it to her while she was dying. (The Snowmen)
At some point farther into their adventures than with other companions, The Doctor gave the original Clara Oswald a key to the TARDIS. (The Time of the Doctor)the Twelfth Doctor had seven keys in his possession, hidden in different places inside his TARDIS. Clara attempted to steal them and blackmail The Doctor into saving Danny Pink. (Dark Water)
BEHIND THE SCENES
The original spade-type TARDIS key was designed by Jon Pertwee and began use in Season 11.
The Rassilon-style key was designed by Mike Tucker.
The prop used for the TV movie was a BBC-licenced replica of the classic spade key, sold at the time by now-defunct American memorabilia catalogue 800-TREKKER.
The 2005 key was a standard nightlatch key made by UK lock manufacturer ERA, and it was the real key to the working lock on the TARDIS prop. Spares were stored in a secret compartment inside the TARDIS prop.