‘ Then Ehud went out into the vestibule and shut the doors of the parlour on him, and locked them.'
The word for vestibule is otherwise unknown and its meaning not certain. But the import is clear, he was able to leave and lock the door behind him.
Wooden keys for crude locking devices are well known. The key would be a flat piece of wood furnished with pins which corresponded to holes in a hollow bolt. The bolt was on the inside and would be shot into a socket in the doorpost, and would be fastened by pins which fell into the holes in the bolt from an upright piece of wood attached to the inside of the door. To unlock the door you would put your hand through a special hole provided (Song of Solomon 5:4), and raise the locking pins by using the pins in the ‘key'.