I recently discovered that even door locks need regular maintenance. This weekend my key would not open the deadbolt on my back door. Having broken off a key in the lock several years ago, I knew better than to force it. With my limited fix-it knowledge I grabbed the screwdriver and took the doorknob off. Unfortunately my efforts were not successful so I ended up calling a locksmith. He spayed it with WD-40 and magically it worked. He said I should lubricate the door locks annually, especially in high humidity areas like Georgia. That was news to me, but it does make sense.
I did some research and learned that a petroleum-based lubricant like WD-40 is not the best choice because an oil-based product attracts dust particles and can gum up the lock. A better choice is a silicone spray, a PTFE (Teflon) spray, or graphite. Spray the lubricant into the keyhole and moving parts of the doorknob and deadbolt. If you have time, take the doorknob and deadbolt apart and lubricate all the moving parts. A few minutes each year will keep your locks in good working order and save you the cost of a locksmith.
For a complete home maintenance checklist visit http://www.fcs.uga.edu/extension/home-publications.