We know that performing routine maintenance now almost always saves trouble and/or expense later. But we are always busy doing something else and tend let things slip, especially things that work without much attention like door hinges and locks. Normally, they will be trouble free for years. As a routine preventive step or at the first sign of trouble, for locks, squirt a few drops of light household oil on a key and work it back and forth and side to side in the lock slot to clean and lubricate the parts. For doors, carefully oil the hinge joints and bolts .This will extend their service life by years. Wipe the oil off the key, lock and hinges when you are finished. While you are at it, be sure to tighten their mounting and set screws to keep them steady and aligned.