玄関

How it works

誰だれ (who) plus か (some-) makes 誰かだれか (someone) — when か (question) attaches to a question word it turns it indefinite. The location 玄関げんかん (entrance) is marked by に (at), which here pins down where something exists. The verb いる (is (animate)) is used for living beings, so the line means "someone is at the door".