The Cloister Bell is a signal to the crew that a catastrophe that could threaten even a TARDIS is occurring or will soon occur. In short it is a call to "battle-stations." Cloister Bells can be found on all TARDISes since the Type 22.
The bell will ring for events ranging from is the phasing of the TARDIS engines, to the detection of a vortex discontinuity, to the imminent heat death of the universe. Though it is located in the Cloister Room, the Bell can be heard from anywhere in a TARDIS. Normally controlled by the Main Logic Junction, the Cloister Bell is linked to the flow of the Universe and thus able to predict many disasters before they occur. Even when the TARDIS Sentient Matrix is unconscious the Main Logic Junction can still trigger the bell. The Cloister Bell can also be manually rung from the Control Room by crew members The High Council of Gallifrey can send a signal that will cause every Cloister Bell in the Universe to ring.
The following color code is used:
- Black: For information from the TV Series, including Dimensions in Time, and 1996 TV Movie.
- Blue: For information from the Novels and Audios including Target, Virgin, BCC, and Big Finish.
- Green: For information from 'licensed' reference sources such as the Technical Manual, Doctor Who Magazine, and the Role Playing Games.
- Red: For information from unofficial sources -The Faction Paradox series, behind the scenes interviews, author's speculation, and popular fan belief.
The TARDIS Technical Index is copyright Will B Swift.