A flap barrier, also known as a flap gate or flap turnstile, is a type of pedestrian access control system commonly used in areas where there is a need to regulate the flow of people, such as transit stations, office buildings, stadiums, and other public venues. Flap barriers consist of a series of rotating arms or flaps that are mounted on a central axis. These arms or flaps can be made of metal or transparent materials like acrylic or glass. They are typically designed to rotate in one direction only, allowing pedestrians to pass through one at a time.