The hill-holder was invented by Wagner Electric and manufactured by Bendix Brake Company in South Bend, Indiana.
In layman’s terms, the modern hill-holder function works by using two sensors, in concert with the brake system on the vehicle.
The first sensor measures the forward-facing incline (nose higher than tail) of the vehicle, while the second is a disengaging mechanism.
To disengage the system and move the car forward, the driver selects first gear, gently depresses the gas pedal, and slowly releases the clutch pedal which at a point in its travel releases the braking system, allowing the car to proceed.
Hill-holders work best for those who are inexperienced with manual shift techniques, or in situations with heavy traffic in steep hilly conditions (as in San Francisco, or Duluth for example).
Cars equipped with a parking brake pedal are not suited for this maneuver unless it is released by hand, for example in the Citroën XM.