MK3 Emergency transceiver

A MK3 Emergency transmitter was a part of the TARDIS that the Fourth Doctor had never used before. While cleaning out number four hold, Romana II found it, and the Doctor said it was a "just a piece of junk". K9 said the Doctor had never used it before, and Romana said it was because he kept getting calls from Gallifrey. The Doctor then allowed Romana to plug it in. It picked up a distress signal from the planet Chloris. (TV: The Creature from the Pit)