Closets, cabinets, under/behind/inside literally everything you own. A hatchling BP can fit nearly anywhere, so leave no stone, pantry, or couch cushion unturned. If you have tile or non-carpet flooring, one method is to put flour down between rooms so you can see if the snake has been through.

But seriously, I mean it when I say it can be literally anywhere. Don't be surprised if it finds itself inside a light fixture or up under a sink somewhere.