Seventh Doctor's sonic screwdriver

The Seventh Doctor acquired a sonic screwdriver at an unspecified point of his life. Many contradictory accounts existed, including one which claimed he had acquired it at some point before meeting Bernice Summerfield, (AUDIO: Love and War) and another, which claimed he acquired it from himself on a parallel Earth where the species Homo Reptilicus had conquered the Earth and killed his third incarnation. (PROSE: Blood Heat, First Frontier) The Doctor himself claimed that he had only recently built one shortly before re-encountering, (PROSE: No Future) and that he received it as compensation after suing the Terileptils for criminal damage; (PROSE: GodEngine) the Terileptils having destroyed the sonic screwdriver used by the Fifth Doctor. (TV: The Visitation) The Eighth Doctor claimed that this screwdriver was a spare model that had "rolled under the TARDIS console and remained there" until the Seventh Doctor found it. (PROSE: Frontier Worlds)

This model, identified as the "Mark 5" by the Eighth Doctor, (PROSE: Alien Bodies) looked similar to the screwdriver used up until his fifth incarnation: it was silver with a brass trim ring in the lower grip and a handle that resembled that of the previous sonic screwdrivers', now with a flat base. Its upper section was able to undergo telescopic collapse for ease of carrying, and, at its top, it held an emitter with a silver ring and a red bullet-shaped crystal at its centre. (TV: Doctor Who) The Seventh Doctor claimed he patented the sonic screwdriver. (AUDIO: The Unknown) Once, while suffering from amnesia, the Eighth Doctor was able to operate this sonic screwdriver on instinct. (PROSE: EarthWorld) This version remained in the Eighth Doctor's use throughout his life, up until its destruction at the hands of a Cyber-Leader on Earth. (COMIC: The Flood)

The Eighth Doctor had resumed using this model by the end of his life during the Last Great Time War. It was the second and final model the Doctor used thus far that bore an emitter-ring head. (TV: The Night of the Doctor) The Eighth Doctor's other choice of a diode-tipped model would become the standard for his later incarnations. (TV: The Day of the Doctor, Rose, The Christmas Invasion, The Eleventh Hour, Deep Breath)

The Eighth Doctor once commented that he felt undressed without his sonic screwdriver. (AUDIO: The Sontaran Ordeal)

A version of this screwdriver was kept in the Twelfth Doctor's office at St Luke's University. (TV: The Pilot)

Uses
The sonic screwdriver could interact with a variety of locks, including those for caskets, (TV: Doctor Who) doors, (TV: The Night of the Doctor) security gates, (AUDIO: Nightshade) and bank vaults. (PROSE: Trading Futures) It could also open service ducts (AUDIO: Excelis Decays) and create "doorways" in forcefields. (PROSE: EarthWorld)

The sonic screwdriver had a number of scanning functions, being able to analyse energy forms (AUDIO: Nightshade) and bodies for life signs. (TV: The Night of the Doctor) It could perform maintenance on the TARDIS console, (TV: Doctor Who) hack into computers, (AUDIO: The Harvest) melt ice (AUDIO: The Magic Mousetrap) and briefly disable electron bombs. (PROSE: The Tomorrow Windows) It could also disrupt control signals (PROSE: To the Slaughter) and Dalek weapons. (PROSE: Legacy of the Daleks)

The sonic screwdriver affected creatures in sometimes lethal ways, as it could destroy a Dalek's brain when placed against the casing's head (PROSE: War of the Daleks) and was once used to decapitate the King of Beasts. (PROSE: The Adventuress of Henrietta Street) It could also repel ghosts, (PROSE: Vanderdeken's Children) subdue hostile dogs, (PROSE: The Deadstone Memorial) turn Cybermen against each other (COMIC: The Flood) and hold back creatures infected by the Void. (COMIC: The Lost Dimension)