Have you ever given someone a key to something but then later on decided it wasn't such a good idea and you fear that they have copied it, I recently had that problem. There are plenty of lock smiths that will re-key a lock for a fee or you could go out and buy a new door knob. I was running low on cash and decided to take the knob apart and see if there was a way to change the pins (and my key) in a way that the original key wouldn't work. This is my first instructable and is based on what I did. But first, I am NOT responsible for any damage you do to your door knob.