Green’s Dictionary of Slang

open the door n.

[rhy. sl.]

(bingo) the number 44.

1936		(con. 1900s) F. Richards Old Soldier Sahib (1965) 71: No. 44 – Open the Door.
1984		Partridge DSUE (8th edn).
2002		B. Kirkpatrick Wicked Cockney Rhy. Sl.