TARDIS scanner

The TARDIS scanner was the main method for the occupants of the vessel to observe the outside environment. The appearance and specifications of the scanner system varied significantly in the course of the Doctor's travels.

Basic principles and specifications
Most of the time, the scanner system appeared to be a simple optical relay whereby a screen in the console room displayed images from a camera mounted in the outer shell of the TARDIS (indicated on one occasion to be in the light atop the police box). (DW: Enlightenment)

The scanner screen could also display other images and data, like photographs and recorded images or videos. (DW: The Edge of Destruction) On several occasions other powerful individuals were able to commandeer the display screen to display information of their own choosing (most frequently, to allow themselves to communicate with the Doctor). (DW: The Armageddon Factor, The Three Doctors, Resurrection of the Daleks, The Keeper of Traken, Victory of the Daleks)

On these occasions the scanner broadcast sound as well as vision, which was not always the case when it was used to view the external environment.

The scanner screen variously appeared as a small monitor attached to the ceiling of the console room, as a larger screen concealed behind shutters and embedded in the wall itself, and as a smaller monitor incorporated into the main control console.

During the Doctor's sojourn in E-Space, the scanner system suffered from a serious flaw in that, rather than being an optical relay as previously indicated, it displayed an image of the space at the co-ordinates occupied by the ship through some unspecified method.

The absolute value of the co-ordinates was utilised, causing problems in an environment like E-Space with negative co-ordinates (the scanner showed images of Gallifrey while the ship was on Alzarius, the two planets having the same co-ordinates in different universes). The key component in the system was the image translator - inserting an image translator from the local environment rectified the fault. (DW: Full Circle)

When Jo Grant brought a Micro Servo Robot into the TARDIS, it connected itself to the computer and began transmitting adverts. One of these adverts had scanner display adverts. (ST: Pop-Up)

While the TARDIS is invisible, it could not work (at least to the Doctor's knowledge). However, River Song showed Amy and Rory it CAN work when cloaked; she adding a cord from the console to attach to the scanner, which, after sending sparks flying, got it to work. The Doctor figured she would have gotten it working while he was gone and asked her when he was pinned down by the Secret Service; this lead another of their "I hate him", "No you don't" moments. (DW: The Impossible Astronaut)