Quantum Paradox Protection Apparatus

The Quantum Paradox Protection Apparatus, also known as QPPA,

was a form of technology invented by the 13th Doctor in order to protect the user from harmful paradoxes. it was first introduced in the Episode "The Fade" and consisted of a watch (the element of time) and the TARDIS key (an element that had the properties to exist outside if space and time), this apparatus' functions were to shroud the user in a force-field, keeping them safe from harmful paradoxes, or potentially being erased from time.

The Thirteenth Doctor used this Apparatus to protect him from the Ripple Effect in the Episode "The Fade".