Key
From Tardis Wiki, the free Doctor Who reference
A key was an object to open a lock.
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)
John Hart once hid a key in the lining of his throat. (TV: Kiss Kiss, Bang Bang)