The safety brake locks the screen in any position stopping it from automatically retracting into the housing even if accidentally bumped or released. It is the safety brake that makes the our retractable fly screens vastly superior to its competitors. It makes using the retractable flyscreen safer as the handle will not spring back crushing fingers between the handle and the housing. The safety brake will automatically engage when you release the handle in any position along the track. The safety brake makes an enormous difference for large openings as the retractable flyscreen does not have to be opened fully to walk through.