A belay device is a mechanical device used in climbing, canyoneering, and mountaineering to control the rope during belaying. It helps to manage the rope's tension, allowing a climber to ascend or descend safely. The device works by creating friction against the rope, which can stop a fall or lower a climber smoothly. Common types of belay devices include the ATC (Air Traffic Controller) and GriGri. These devices are typically made of metal and are designed to be lightweight and durable. Proper use of a belay device is essential for safety in climbing activities, making it a crucial tool for climbers and their partners.