The knock option consists of extra circuitry added inside the ECU, an extra wire and connector on the wiring harness and the knock sensor itself. Knock control allows the ECU to retard the ignition timing on E and F systems automatically if knocking is detected. This is a good backup to the standard boost retard capabilities of the E and F units for many engines but we don't recommend using the sensor as the primary means of reducing detonation. We also don't recommend this option on most air cooled engines or engines which are mechanically noisy as it can be difficult or impossible to tune out this noise while still allowing the ECU to "hear" actual knocking.