A belay device is a mechanical device used in climbing to control the rope during belaying. It helps to manage the rope's tension, allowing a climber to ascend safely while providing support in case of a fall. Common types of belay devices include the ATC (Air Traffic Controller) and GriGri, each designed for specific climbing scenarios. When a climber falls, the belay device locks the rope in place, preventing the climber from falling further. This safety feature is crucial for both sport climbing and traditional climbing, ensuring that the belayer can effectively manage the climber's safety while they navigate challenging routes.