Hostile Action Displacement System

The HADS (Hostile Action Displacement System) was one of the defence mechanisms of a TARDIS. Upon the outer shell of the vessel coming under attack, the unit dematerialised the TARDIS and rematerialised it a short distance away, in a safer locale. (DW: The Krotons)

The novelization of The Krotons (novelisation) indicates that the HADS must be manually set, and The Doctor often forgets to do so, explaining why the TARDIS often doesn't react to attacks.

The HADS of the TARDIS belonging to Drax could apparently be manually triggered when the vessel was coming under fire, but the account detailing this is probably apocryphal. (Search for the Doctor)

While stuck on Earth and attempting to avoid meeting himself the Fifth Doctor engages the HADS to move the TARDIS. (BFA: The Mutant Phase)