Airlocks are small chambers that separate two different environments and allow the passage of people between these different environments. Generally they contain two airtight doors and a means to equilibrate the environment of the chamber to match whatever area is being entered. Airlocks may sperate the interior of a spaceship from space or may separate the interior of an undersea habitation unit from the waters of the ocean. They may be paired with a decontamination chamber, especially if located on an off-world research station.
When designing airlocks, consider the controls that operate it and where they are located. Often in narratives, airlocks are a means to dispose of a person or an unwanted creature into space.