Etiquette question: Would you ever enter someone else's bedroom without knocking?

You are a guest in someone’s home. You are staying in a guest room, or crashing on the couch. You wake up in the morning, and go to greet your host. The host’s bedroom door is closed.

Do you let yourself in, or knock first? Is there anyone you have a relationship with that is close enough that you would feel comfortable entering without knocking (best friend of many years, sibling, parents)? Does it make a difference if your host has a partner, who is also sleeping in the bedroom behind the closed door?