Gallifreyan calling card
From Tardis Wiki, the free Doctor Who reference
Members of the Winter family were able to summon the Doctor's TARDIS by using a Gallifreyan calling card.
When they were on their worse day on their life, the possessor of the card could use, to bring the Doctor to them. The card was able to track the TARDIS and make it dematerialise, no matter where it was. (AUDIO: The Gods of Winter, The House of Winter, The Sins of Winter, The Memory of Winter)
