Instructions
Look around for male carpenter bees. They hover around the female's nest. Male carpenter bees do not have stingers, but they will try to intimidate you by flying at you and buzzing around your head.
If you notice male bees, look on the ground or on any horizontal surfaces for what appears to be coarse sawdust. This is called frass. It comes from the hole the bee drilled.
Look above the frass, and you should see a perfectly round hole 3/8 inch in diameter. This is the carpenter bee's nest.