Defence Indefinite Timeloop Option

The Defence Indefinite Timeloop Option (or DITO) was part of the TARDIS's safety systems. The Doctor explained that it could be activated automatically by the TARDIS if it detected a threat. It causes the ship to project itself forwards a millisecond in time and remain there, inaccessible to intruders.

It was engaged when the Doctor landed in Oxford and the TARDIS detected the presence of the Garvond. The DITO could be deactivated using Benny's homing beacon. (NA: The Dimension Riders)

The Doctor also manually activated a similar TARDIS capability, trying to stop the Master from discovering it. (DW: The End of Time)