Info taken from Wikipedia:

The sonic screwdriver is a fictional tool in the British science fiction television series Doctor Who and its spinoffs. It is a multifunctional tool used by The Doctor. Its most common function is that of a lockpick, but can be used to perform other operations such as performing medical scans, remotely controlling other devices and tracking alien life. It can, with the exception of a deadlock seal or wooden lock, open any type of lock and operate many computers, whether their origin is alien or human.