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".