Christel Dee's sonic screwdriver

Christel Dee's sonic screwdriver was used by the human young woman during many of her adventures and escapades, not always for its intended use.

An unlikely baton
While reporting on the Doctor Who Fan Orchestra and the then-upcoming Australian Doctor Who Symphonic Spectacular for the viewers of The Fan Show, Christel Dee used her sonic screwdriver to conduct a large orchestra which provided the incidental music for her video, live. (NOTVALID: The Universal Song Contest & Symphonic Spectacular!)

Infiltrating Baker Street
Still for the sake of The Fan Show, Christel later penetrated the defences of Steven Moffat's secret writing lair carved out in a hollowed-out volcano beneath 221B Baker Street. In this endeavor, Christel's sonic screwdriver was invaluable to her: she used it, in quick succession, to reverse the polarity of the neutron flow of the security panel, to disengage the Hostile Action Displacement System, to neutralise the siege mode protocols, and to quantum-lock the underground lava pool. As she used it, the screwdriver buzzed loudly and glowed with a faint blue light. (NOTVALID: Stealing Series 9 Scripts)

The Chameleon Arch
When Christel planned to go on holiday to Barcelona by borrowing the Doctor's TARDIS, her friend Ben tried to surprise her by uploading a new, Minecraft-themed desktop theme to the Ship's databanks. Due to a malfunctioning chronon link, the TARDIS ended up forming a temporal Chameleon Arch around Christel, warping her dimensions to "fit" the desktop theme. Hence, Christel found her body transformed into a walking, talking Minecraft-avatar version of the Tenth Doctor — and, with it, her sonic screwdriver was transformed into a blockier version of itself, now with a green "bulb" as its tip.

However, this did not impair the efficiency of the device, which, indeed, proved Christel's salvation: on Ben's advice, she used it to correct the chronon link, successfully flying the TARDIS back from Minecraftia to England where she started from. As she stepped out of the TARDIS, Christel herself returned to normal as well, as did her attire and accessories. (NOTVALID: Doctor Who Minecraft)

Behind the scenes

 * Christel Dee's sonic screwdriver is more-or-less visually identical to the Eleventh Doctor's sonic screwdriver as seen on television from The Eleventh Hour onwards, with the exception of its glowing blue in Stealing Series 9 Scripts.