We have spoken at some length on various tools that can be used to bypass locks. At JTT, we consider this to be an important skill that any responsible person should be familiar with. I recently came across an interesting tool, the Killer Key, that does the opposite of bypassing a lock: it can actually lock it permanently. The ability to control access like this may be just as important as the ability to bypass a lock.
The Killer Key is simple to use. It is scored so that the user inserts it into a lock and bends it, a section of the key breaks off and remains lodged in the keyway. It has a large notch that allows the pins in the lock to drop which effectively locks the broken section in place, permanently disabling the lock. This locks out those on the exterior of the structure but can not lock in people on the interior.
The Killer Key is available for Schlage® or Kwikset® keyways which covers a vast majority of the key styles in the USA. This seems like it could be a valuable addition to an E&E or urban survival kit.
Check out the Killer Key on VigilantGear.com.