The Ultimate Safety Net: What is a Dead Man’s Switch (Vigilance Device)?

Also known as the Vigilance Device or Alerter, the Dead Man’s Switch is a fail-safe mechanism designed to automatically apply emergency brakes if the train driver becomes incapacitated, falls asleep, or loses consciousness.

The Ultimate Safety Net: What is a Dead Man’s Switch (Vigilance Device)?
December 8, 2025 11:08 am
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The Dead Man’s Switch (often called a Vigilance Device or Alerter) is one of the oldest and most critical safety features in railway history. Its primary function is simple but vital: to ensure that the human driver is present, conscious, and in control of the train.

Why is it Called “Dead Man’s Switch”?

The grim name comes from its original purpose: to stop the train if the driver died or became incapacitated (e.g., heart attack, fainting) while driving. In modern terms, it is more commonly referred to as a Vigilance Control System.

How It Works

The system requires the driver to send periodic signals to the onboard computer to prove they are alert. This is usually done by:

  • Keeping a foot pedal pressed (and briefly releasing it periodically).
  • Pressing a specific button on the dashboard.
  • Interacting with controls (horn, throttle) which resets the timer.

The Emergency Sequence

If the driver fails to interact with the system within a set time (usually 30 to 60 seconds), the system initiates a safety sequence:

  1. Visual Warning: A light flashes on the dashboard.
  2. Audible Alarm: If no reaction occurs, a loud alarm sounds.
  3. Emergency Braking: If the driver still does not respond, the system assumes incapacitation, cuts power to the engine, and applies the emergency brakes to stop the train.