A temporal transport beacon was a device utilized by Starfleet in the 29th century, for use in obtaining a pattern lock on individuals who had traveled through time using a temporal transporter.
A temporal transport beacon was given to Seven of Nine, who was recruited from the year 2375 by the crew of the USS Relativity, for a mission to prevent a saboteur from destroying the USS Voyager. Lieutenant Ducane ordered Seven to re-calibrate her temporal transport beacon, as her proximity to a force-3 temporal disruptor resulted in a level of interference which would endanger Seven's life if she were to be transported. (VOY: "Relativity")