Distress signal receiver

The distress signal receiver was supposedly a component in the Doctor's TARDIS that let the Doctor pick up SOSes from anyone, anywhere. Although he never knew who sent them, he always answered them. (TV: The Sontaran Experiment, Planet of Evil, The Creature from the Pit, Battlefield, Attack of the Cybermen, Terror of the Vervoids, Dalek, 42, The Curse of the Black Spot)

The distress signal receiver was located on the TARDIS console. (TV: Planet of Evil) On at least three occasions, it was the psychic paper that received the distress signals. (TV: New Earth, Silence in the Library, Night Terrors)