Sonic penny whistle

The Doctor's sonic penny whistle is a sonic device/flute-like musical instrument created within the TARDIS console room, either by the Doctor or the TARDIS itself. It is modelled after a Meg by Clark's D penny whistle.

History
The Doctor unwittingly put the sonic penny whistle in between his waist and trousers, tucked under his shirt sometime prior to entering the mysterious house of Morlog. This was likely done sometime between his waking from regeneration and his leaving the TARDIS and inevitable capture. When he was about to be mentally pierced and controlled by Morlog, he felt the device digging into him and used it to reverse the effects, banishing Morlog between dimensions and playing a tune as he left the woods and entered the TARDIS (The House of Morlog).

When the Doctor found out that the house in Somerset was being used as a colony for the Daleks, he played a tune while figuring about how to defeat them and used the sonic penny whistle to rewire an old fashioned radio and connect it to the Daleks' main computer. The resulting chain of explosions destroyed every active Dalek in the colony. As he left the Spy Dalek, he played his penny whistle, oblivious to the fact the Dalek was alive and signaling for help (Colony of the Daleks).

When the Doctor landed in Devon in 2018, he used the device to shrink the TARDIS down to a size small enough to fit in the Doctor's pocket. Later on, he used it to dry himself and make his way into Towell Farm. After wondering around, he found the Basement Entity and tried to sooth it, but instead found himself playing a tune to destroy it with. After being near energised to death, the Doctor used the TARDIS to overpower Scooter 2000 and finally used the penny whistle's sonic feature to blow the robot to pieces. After returning to the open countryside, the Doctor used the penny whistle to grow the TARDIS back to normal size and continue his journeys throughout time and space (Horror at Towell Farm).

Trivia

 * The penny whistle originally belonged to Astile's aunt, Rhiannon, who reluctantly sold it to him for £20 and was glad to hear he hadn't lost it when he played it down the phone during editing of The House of Morlog.
 * The usage of the penny whistle as a device and musical instrument is obviously a homage to the Doctor's various sonic screwdrivers and the way the Second Doctor played a recorder.
 * It is difficult to play when out of breath.
 * Yasara (who helped film The House of Morlog) does not like the penny whistle, and finds it annoying and embarrassing, especially in public.