A descender or rappel device is a friction device or friction hitch that allows rope to be payed out in a controlled fashion, under load, with a minimal effort by the person controlling it. The speed at which the abseiler descends is controlled by applying greater or lesser force on the rope below the device or altering the angle at which the rope exits the device. Descenders can be task-designed or improvised from other equipment. Mechanical descenders include braking bars, the figure eight, the abseil rack, the "bobbin" (and its self-locking variant the "stop"), the gold tail, and the "sky genie" used by some window-washers and wildfire firefighters. Some improvised descenders include the Munter hitch, a carabiner wrap, the basic crossed-carabiner brake and the piton bar brake (sometimes called the carabiner and piton). There is an older, more uncomfortable, method of wrapping the rope around one's body for friction instead of using a descender, as in the Dulfersitz or Geneva methods used by climbers in the 1960s.
[Wikipedia]