Abstract: A belay device for protecting a climber on a rope from a fall has a powered winding reel to which the rope is attached. A control mechanism acts to prevent slack in the rope between the climber and the winding reel and includes load sensor that which, on detecting the weight of the climber on the rope, switches the operation of the device to a fall or descent mode where the winding reel is stopped and the climber is suspended by the rope. An electronic control and diagnostic system monitors the operation of the winding reel and switches its operation to a safe, fault mode when a fault is detected.