Even though you realize your home is not an impregnable fortress you probably still put locks on your doors and windows. They won’t keep a determined intruder out but they should slow him down and/or force him to make some noise to break in. However, if you didn’t pay a premium for your locks then odds are they can be opened in seconds by even an unskilled child using a simple method known as bumping.
Granted, locks alone don’t secure a house, but they should at least put up a fight. If you are robbed and there is no sign of forced entry you will have a hard time getting an insurance payout.
Bump-resistant locks will cost at least $100 apiece. I bought a set of Medeco Maxum deadbolts here at that price.
2013 Update: KwikSet SmartKey locks are also bump-proof, sell at big-box stores for $30, and can be rekeyed without a locksmith. I equipped my current house with these. I have seen some complaints that the locks can “fail” and need to be reprogrammed, but so long you have more than one keyed entrance that shouldn’t be a big problem given how cheaply and easily they can be replaced. Hackers have also found a clever way to decode these locks, but it takes minutes, after which they have to cut a key. So it is possible a skilled attacker with unguarded access to your lock could make an unforced entry to your house. In contrast, locksmiths tell me that the only reliable way to open a Maxum or Primus lock without the key or code is to drill it (which is expensive, noisy, and time-consuming).