The Doctor's signet ring
Talk about it here.
He discarded it after his regeneration into his second incarnation, as it did not fit him any longer. (TV: The Power of the Daleks) Eventually, the Doctor became more reliant on his sonic screwdriver. (TV: Fury from the Deep)
It was discovered to have fallen into the TARDIS console following the Doctor's first regeneration, where it remained until it was recovered by his seventh incarnation, who decided to start wearing it again. (COMIC: The Chameleon Factor)
After wearing it through numerous adventures, (COMIC: The Good Soldier, Metamorphosis, PROSE: Tragedy Day) the Doctor gave the ring to Joan Redfern after he turned back from being John Smith. (PROSE: Human Nature)
The ring had several special abilities. It could supply power to the TARDIS's main doors and control a Zarbi. (TV: The Web Planet) If given the correct spectrum of light, it could unjam a TARDIS's locking mechanism. (TV: The Daleks' Master Plan) The ring seemed to be able to facilitate hypnotism and protect the Doctor from electrical shocks. (TV: The War Machines) On the Ethereal homeworld, the Doctor used the ring to open an electronic lock. (PROSE: The Cloud Exiles) When the Doctor received lessons in the "magic" of Avalon from Kilvenny Odoyle, the ring served as his "wand" through which he focused his spells. (PROSE: The Sorcerer's Apprentice)
Behind the scenes Edit
The ring plays an important part in Doctor Who: Legacy's Sonic Adventure storyline. In it, the Master steals all of the sonic devices onboard the TARDIS and scatters them through time. The ring was not stolen because it contained no sonic technology, but the First Doctor could still use it like the other Doctors used their screwdrivers and used it to get back all the sonic devices.