Cloister Bell

The Cloister Bell was an alarm bell, located in the Cloister Room inside a TARDIS.

It went off when the Master cannibalized The Doctor's TARDIS into a Paradox Machine.

When the Cloister Bell tolled, it sounded like a big church bell. (DW: Logopolis)

In Attack of the Graske the cloister bell sounded along with a light on the Console as a warning to an approaching teleport.