A related option to allow entry based on a code, if you don't want to replace your lock, is to put a combination key lock box (sometimes called a "realtor box") somewhere near the door. We have one of these and have been very happy with it. And no batteries that can die!
One threat model with that kind of approach is that once a visitor possesses your key -- even if they return it -- you can't tell how many copies they may have made.
