How do modern engines detect and prevent knock?

Knock is detected using piezoelectric knock sensors that detect the characteristic vibration frequency (typically 6-15 kHz) of abnormal combustion. The ECU analyzes the signal in specific crankshaft angle windows when knock is expected. When knock is detected, the ECU retards ignition timing for affected cylinders until knock stops, then gradually advances timing to optimize performance. Modern systems use individual cylinder knock control and ion-sensing through spark plugs for faster detection.