A bump key is a device used to gain entry through a locked door using without damage to the door or the lock itself. http://www.lockbumping.org/

A bump key, or 999, is a key which means that all of the grooves on the key are filed down to the deepest setting on the key.Snopes.com: Bump Keys The key is then used to "bump" the pins in a standard door lock, while using enough pressure to turn the cylinder, thus opening the door. While some report it is not as easy as it looks, others report than any 10 year old child could do it.http://www.lockbumping.org/ The technique was developed by a locksmith in Denmark in the 1970s. Tumbler styled locks have been in use for hundreds of years, and only now are companies coming up with advanced lock techniques that will prevent the use of the bump key. Bump-proof locks are more expensive than a standard door lock, costing approximately $150.

Because bump keys leave no sign of forced entry, insurance companies may not believe that there has been a theft, and have been known to refuse to pay claims after a lock bumping incident.http://www.lockbumping.org/