Key

A key was an object to open a lock. In emoji, 🗝️ was the symbol used to denote the unlocking of a door or object. (TV: Smile)

The Doctor's toolbag contained, among other things, a set of keys. (TV: Doctor Who)

A TARDIS key allowed access to a locked TARDIS, regardless of the form taken by the outer plasmic shell. (PROSE: Interference - Book Two)

Katarina, a Trojan from circa 1200 BC, was unfamiliar with the concept of a key. The First Doctor used his own key to explain what one was to her. (TV: The Daleks' Master Plan)

John Hart once hid a key in the lining of his throat. (TV: Kiss Kiss, Bang Bang)

Behind the Scenes
The TARDIS Sound was created by rubbing a housekey along a piano wire.