Oddly enough, the next item in this little series isn’t a weapon, not really. It really is more of a tool, but that doesn’t stop the universally renowned (and in some cases, feared) Doctor from Doctor Who, from wielding it like one.
In fact, against regular organic beings, the sonic screwdriver is completely harmless. Now, you may be thinking to yourself Ok, so if that’s the case, what makes it such a deadly weapon? As it turns out, this little device is quite versatile, making it a handy commodity in any arsenal.
The primary purpose of the sonic screwdriver is to unlock or lock doors. As the Doctor and his companions are often seen running away (which to be fair, buys them time to come up with a plan to overcome the threat du jour and win the day), this comes in quite handy. It also makes infiltration and investigation a bit easier.
In addition to that though, the screwdriver has an array of uses. It can scan for things (energy, life signs etc.), and it can do wonders with electronic equipment. Depending on what the Doctor needs it to do, the screwdriver can repair machines or it can just as easily destroy them.
This is convenient as two of the Doctor’s biggest enemies (the Daleks and the Cybermen) are heavily machine based, meaning that he can use the device to fend off a potential oncoming attack if he needs to.
It is also helpful when working with computers as he can search through large arrays of files much quicker by just flashing the screwdriver at the monitor than by trying to acquire the information manually.
Beyond this though, the uses of a sonic screwdriver vary from era to era. Some writers try to intentionally limit the functionality of the device (heck, some featured Doctors who NEVER used a sonic screwdriver) while others go hog-wild, letting the device do whatever the plot needs it to (such as lighting candles, reattaching two ends of a piece of cut barbed wire, or unraveling a piece of rope).
As for the current iteration used by the eleventh doctor, it’s an odd mix of both. It does have a variety of functions, generally doing whatever the Doctor (or the plot) needs it to, but they have placed some explicit limits on it. For example, the current version of the sonic screwdriver doesn’t work on wood.
A lot of times, characters will poke fun at the fact that the Doctor carries around a high tech screwdriver as opposed to a more traditional weapon, but he’s been able to face tremendous challenges with nothing more than said screwdriver and his wits. It may not be as offensively potent as the other weapons discussed, but it can come in quite handy in tight situations.