Abstract: A method, and apparatus for carrying out the method, for detecting knocking operation in externally auto-ignited internal combustion engines. The radiation emitted from the combustion chamber gases is detected with a knock sensor and is passed on. Suitable as a knock sensor are photo-conductive fibers which are preferably accommodated in the central electrode of the spark plug. The radiation detected by the knock sensor is conveyed through a transmission mechanism, which can also be constructed of photo-conductive fibers, to a radiation receiver and a signal converter, for example a photo-multiplier, and is subsequently processed in a processing logic. The processing logic delivers an output signal when knocking operation exists. This output signal can either be indicated, and/or can be utilized to control the parameters which influence the knocking combustion.