A sonic screwdriver is a fictional item used in the television series Doctor Who. Within the television show, the exact function of the device is somewhat mutable. The device has very little relationship to the tool traditionally thought of as a screwdriver and can perform various functions, including unlocking locks, taking various readings, and welding. Of course, a tool that can be used to solve any problem is a major stumbling point for effective plot development. For this reason, the screwdriver is often given strange and unusual limitations in order to prevent the device from resolving the story.
First introduced in the Doctor Who series in 1968, the sonic screwdriver was used with variable frequency for many years. It only became a true focal point of Doctor Who when the series was reincarnated in 2005. While it has been suggested that the Doctor has had a sonic screwdriver since childhood, the device was taken out of the show in 1982 and did not appear again in the original series.
There have been many different designs of the sonic screwdriver through the television series, each looking quite different. In addition to these many devices, there have also been spin-off devices that serve similar functions, such as the sonic lipstick from the Sarah Jane Adventures. Each screwdriver is similar but not entirely the same, and some perform improved functions over previous models. The Doctor uses the screwdriver in a number of ways, but most of the time these involve pointing the device at the object being acted upon.
Although the complete functions of the sonic screwdriver have not been revealed within the series, its primary function seems to be similar to that of a lock pick. It also frequently provides diagnostic information, though it is not always clear how precisely this information is obtained. Within the new series, the screwdriver has been shown to interact with phones and computers several times, sometimes reprogramming them to work in different ways. In general, the functionality of the screwdriver is not explained, and the term sonic does not relate directly to the jobs performed by the screwdriver.
As a tool in the Doctor's arsenal, the sonic screwdriver is problematic for writers of the show. Sometimes, limitations are placed on the screwdriver in order to prevent the tool from solving essential plot problems. For example, it has been noted that the screwdriver does not work on wood, which is an obstacle that was introduced in "Silence in the Library" in order to create tension when trying to open a wooden door. The writers of the series recognize the somewhat ridiculous nature of this device and often poke fun at the tool within the show.