The sonic screwdriver has been part of the Doctor's arsenal since the second Doctor's adventure 'Fury form the Deep'.
I most vividly remember Tom Baker using it to unscrew a table in the 'Ark in Space', but it's been used for a variety of reasons. It seems to be have gone out of favour the further on the fourth Doctor's reign went on but was resurrected for the Nu-Who, and is used heavily by David Tennant.
Here's the Wiki's fact based take on the Sonic Screwdriver
The sonic screwdriver is a fictional tool in the British science fiction television series Doctor Who and its spinoffs. Its most common function is to operate virtually any lock, mechanical or electronic, but excluding those made from wood. It has also been used for repairing equipment. Like the TARDIS, it has become one of the icons of the programme and is closely associated with the Doctor.