Timey-wimey distress beacon

The Timey-Wimey Distress Beacon was built by River Song on the top of the Great Pyramid of Giza in an alternate timeline where all of history occurred at once. The timeline came into being because she refused to kill the Eleventh Doctor. She used the beacon to send a message to all space and time asking for help on behalf of the Doctor. (DW: The Wedding of River Song)