Airlock

Airlock
Examples of closed (top) and open (bottom) airlocks. The middle design is the standard 1x2 airlock, while the left and the right are the scalable airlock model, which can be any size.
Properties

Airlocks can be open or closed without exposing a starship to the vacuum of space.
Airlocks can be detected with the sign text [airlock].
Right clicking the sign toggles the airlock by converting the iron bars to a portal.