There is currently a lot of buzz on the Internet about the emerging threat of “lock bumping.” 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. And here is another video, from here in the States. My advice is to upgrade the locks on your exterior doors with top quality locks made by Medeco or Schlage Primus. 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 or the not quite so expensive Medeco “C” and “E” series padlocks.) 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, that typically sell for around $60.