What is a pass key security system?

The Pass-Key, Pass-Key II, or VATS, as it's called in earlier GM vehicles, uses a resistor mounted in the key blank to confirm that the correct ignition key is being used to start the engine. Many people call the resistor pellet a "chip" due to the common misconception that it is some sophisticated digital circuit to identify the key to the car. Not quite. It is not a "chip" of silicon as is customarily used for integrated circuits, but merely a block of carbon appropriately sized to have a desired electrical resistance.