Cloister Bell

The Cloister Bell is an alarm bell located in the Cloister Room inside a TARDIS. The Cloister Bell is to be used in the most serious and utmost emergencies. Its distinctive, sonorous ringing sounds resembles that of a large church bell. It could be answered by anyone inside the TARDIS, and the Doctor told Adric that if he needed him, Adric could sound the Cloister Bell. (DW: Logopolis)

The Doctor's TARDIS

 * The Bell sounded as the Doctor crashed the TARDIS (DW: Children in Need).
 * The Cloister Bell sounded continually went off when the Master cannibalized the Doctor's TARDIS into a Paradox Machine. (DW: The Sound of Drums)
 * It also sounded when the TARDIS of the current Doctor and one of his past selves crashed together. (DW: Time Crash)