Stattenheim remote control
A Stattenheim remote control is a device used by Time Lords to control their TARDISes after linking them to it.
The Rani's remote looked like a black remote with one button (TV: The Mark of the Rani) while the Second Doctor's one looked like a small rod with a recall disc one side and gold prongs on the opposite one to put it inside the teleport control dome of his TARDIS console. (TV: The Two Doctors)
The Master created one to retrieve his TARDIS. (PROSE: First Frontier) The act of whistling was not technically required, but was useful to focus the mind to "call" the TARDIS to the user's location. (PROSE: Timewyrm: Exodus)
The Second Doctor's teleport control where he stored the recall disc of the remote gave dual control of his TARDIS to the Time Lords (TV: The Two Doctors) on Gallifrey. (AUDIO: The Black Hole)
When the Sixth Doctor asked the Second Doctor where he had got a Stattenheim remote control, the Second Doctor said that "Some of us have earned these little privileges." (TV: The Two Doctors) According to one account, the Second Doctor had been granted his remote control by the Celestial Intervention Agency. (PROSE: World Game) According to another account this remote was given to him by the Monk who stole it from Pavo, in order to get the Doctor away from himself. (AUDIO: The Black Hole)
Following the defeat of Chessene and the Sontarans' plans to use the Kartz-Reimer module, the Second Doctor held the Stattenheim remote control and whistled. His TARDIS then rematerialised at the Spanish hacienda he was in. (TV: The Two Doctors)
The Master once tried to steal the Second Doctor's remote control. (GAME: Destiny of the Doctors)