A deadman's device (officially known as a Driver’s Vigilance Device or DVD) is a critical fail-safe mechanism designed to stop a train automatically if the operator becomes incapacitated, falls asleep, or leaves their post. In its simplest form, it is a pedal or handle that the driver must keep pressed down. If pressure is released, the emergency brakes engage. Modern systems are more sophisticated and use a "Vigilance Control" method, which requires the driver to perform an action—such as pressing a button or moving a lever—at regular intervals (often every 30 to 60 seconds) in response to a flashing light or an audible chime. If the driver fails to acknowledge the prompt within a few seconds, the system assumes the driver is unresponsive and initiates a full emergency brake application to bring the train to a safe halt. This device is a standard safety requirement globally and has prevented countless accidents that could have resulted from medical emergencies like heart attacks or simple driver fatigue.