There is currently a lot of buzz on the Internet about the emerging threat of “lock bumping.” [1] This is an old technique used by burglars that can defeat up to 80% of typical household dead-bolt locks. It is catching on with a whole new generation of burglars in the U.S., Canada, and in Europe. (Using an easily obtained specially cut generic “bump” key and a small mallet.) This video clip from Holland (with English subtitles) shows the technique [2]. And here is another video, from here in the States. [3] My advice is to upgrade the locks on your exterior doors with top quality locks made by Medeco [4] or Schlage Primus [5]. These have special cylinders that are engaged by “double cut” or “side-milled” keys. These bump-resistant and pick-resistant locksets cost about $150 each.
Regardless of the locks that you use, it is essential that you never let your keys out of your personal possession, since a large number of burglaries are accomplished by means of illicitly copied keys. Never give a parking valet your entire ring of keys. Never lend your house key to a tradesman. (You should always be there personally to supervise work in your home, regardless.) If you hire a maid, a cleaning service, or a nanny that must have a house key, then do a thorough background check on that individual. And if you have the slightest suspicion that your key might have been compromised, then have your door locks re-keyed immediately. OBTW, the bump technique can also defeat most padlocks. But fear not–ultra high security padlocks with double cut keys are also available. (For example, the $180+ Sargent & Greenleaf #833 [6] or the not quite so expensive Medeco “C” and “E” series padlocks [7].) I should also mention that the real bargain on the market is the U.S. Army surplus arms room padlock (made by Sargent & Greenleaf), often available via eBay, from Coleman’s Surplus [8], that typically sell for around $60.