Sonic screwdriver

The sonic screwdriver is a tool and defensive weapon used by the Doctor from his second incarnation onward. It is also part of toolbox for the Doctor's TARDIS. The Doctor's tenth incarnation sometimes referred to it as "the sonic".

Mark I
A small, simple device very like a penlight. It was first introduced by the Doctor in his second incarnation. (DW: Fury from the Deep)

Uses:
 * Opening up hatches and panels (DW: Fury from the Deep, The War Games) and control panels. (DW: The War Games)
 * As a conventional screwdriver (without touching the screws). (DW: The War Games). *For cutting through a section of a wall. (DW: The Dominators):

Mark II
A larger and more elaborately detailed version, the Doctor introduced in his third incarnation. During his fifth incarnation it was destroyed by the Terileptil leader. (DW: The Visitation). By his seventh incarnation the Doctor had a new one. (DW: Doctor Who: The TV Movie).

Uses:
 * As a means to open the shed containing garage containing the Doctor's TARDIS and Bessie.(DW: Inferno)
 * Detector to discover booby traps in the Master's TARDIS. (DW: Colony in Space)
 * Detecting and setting off land mines from a distance. (DW: The Sea Devils)
 * To open an electronic door. (DW: The Mutants,
 * Undoing wrist clamps. (DW: The Mutants)
 * Detection of anti-matter. (DW: The Three Doctors)
 * To make methane flammable and set off fires. (DW: Carnival of Monsters)

Mark III
In his ninth incarnation the Doctor had a new model with a glowing blue laser-like beam at one end.



Uses;
 * Detecting and stopping telepathic signals. (DW: Rose)
 * Interfacing with a computer. (DW: The End of the World)
 * As a medical scanner and diagnostic tool. (DW: The Empty Child)
 * Battery charging. (DW: Father's Day)

Marks IV and V
The tenth incarnation of the Doctor had a model similar to the previous one, though somewhat larger. It was burnt out after modifying an X-Ray scanner to give off more radiation to defeat a Slab, but was replaced soon after with an identical model.
 * To transfer its powers to the viewer's remote control. (DW: Attack of the Graske)
 * As a lighter. (DW: The Girl in the Fireplace)
 * To partially re-constitute Ursula Blake. (DW: Love & Monsters)
 * Blowing doors open. (DW: Doomsday)
 * Increasing the radiation in a device such as an X-Ray scanner .(DW: Smith and Jones)


 * Mark designations used purely for convenience. The Doctor and others only referred to the tool as "the sonic screwdriver".

Other sonic screwdrivers

 * Liz Shaw had her own sonic screwdriver which she used to open the Doctor's TARDIS for him. (DW: Inferno)


 * This appeared like the Doctor's Mark II.


 * Romana constructed her own sonic screwdriver. The device impressed the Doctor, and he attempted, unsuccessfully, to swap sonic screwdrivers with her. (DW: The Horns of Nimon)


 * This resembled a smaller, slimmer version of the Doctor's Mark II.

Technology and Functions
The sonic screwdriver is apparently the product of Gallifreyan technology since other Time Lords (i.e. Romana) use the device and understand it enough to construct their own versions of it. The name of the device itself suggests that it functions using soundwaves, although the actual workings of the device have never been explicitly explained.

The different versions of the Doctor's sonic screwdrivers have exhibited different capabilities and uses. The device has been mainly used as a repair tool and as a lock picker. Although it is primarily a tool, it can also be used as a defensive weapon. However, according to the Tenth Doctor, the device cannot be used to wound or kill living things. (DW: Doomsday)