TARDIS self-destruct

The TARDIS self-destruct, or self-destruct mechanism, was a system which allowed a TARDIS to trigger its own destruction.

History
During the Last Great Time War, one Battle TARDIS's self-destruct was activated telepathically by the Sensorites, on Gallifrey's orders, as the Daleks had taken control of that TARDIS, among others, to seize the Time Lords' major power source, the Eye of Harmony. (AUDIO: Sphere of Influence)

The Doctor's TARDIS
To escape the realistic dream-world conjured up by the Dream Lord, the Eleventh Doctor activated his TARDIS's self-destruct, causing himself and his companions to "die" and wake up in the real world. This suggested that as far as the Doctor knew, there did exist a functional self-destruct mechanism in his own TARDIS. (TV: Amy's Choice)

The same incarnation of the Doctor, on two occasions, use the self-destruct as an empty threat. During the Ironside Incident held up a Jammie Dodger to the Daleks, claiming it to be a portable remote trigger for the TARDIS self-destruct, which would destroy both his ship and theirs. The New Paradigm Daleks's sensors were sophisticated enough that they soon declare the device "non-existent", with the Doctor admitting to the biscuit's true nature and eating it. (TV: Victory of the Daleks)

The Doctor again used a fake self-destruct sequence to convince the Van Baalen brothers to help him find and save Clara Oswald, who was trapped somewhere within the TARDIS. They had one hour to find her, "until this ship blows". This one was more convincing, even counting down menacingly on a monitor. (TV: Journey to the Centre of the TARDIS)

After admitting it to be a ruse, the Doctor elaborated on his tactics: "I just wiggled a few buttons. Yeah, the old wiggly button trick. And the face. You've got to do the face. "Save her or we all die.""

- Eleventh Doctor