Also called Descenders, Belay and Rappel devices are a necessary tool for any climber. Whether it be on a climbing wall, ropes course, or even up on the mountain, descenders are a handy tool. Basically, a descender is a simple tool which permits the climber to adjust the speed of their descent in a safe manner. Belay and Rappel devices can be as simple as a metal ring to a Figure 8, but there are many types of Descenders to choose from.