TARDIS magnet
From Tardis Wiki, the free Doctor Who reference
The TARDIS magnet was a pocket-sized device with a green light on it. Using it, people could find their way back to the Doctor's TARDIS.
In a featureless desert on the planet Aridius, the Doctor gave Ian Chesterton the TARDIS magnet to ensure he and Vicki could find their way back to the ship after exploring. (DW: The Chase)
