Home Box

Home Boxes were present on Galaxy class starliners in the 51st century. They were described by the Eleventh Doctor as being like 'black boxes' on aeroplanes. When something went wrong on one of these ships, the Home Box was ejected and returned to the home planet with all the flight details.

River Song graffitied "Hello sweetie" in High Gallifreyan onto the Home Box of the Byzantium to contact the Eleventh Doctor, knowing he would one day find it in a museum. (TV: The Time of Angels)