The knock detector has a vibration sensor formed by fixed connection of an annular piezoelectric element (5) with electrodes (5a,5b) on its opposing surfaces to a surface of a thin metal plate (6). A carrier bolt (9) passes through the centre of the thin metal plate. The detector is arranged in a housing mounted on the engine. The housing resonant frequency is essentially equal to the engine's knock frequency.An elastic connection part (11a) is arranged between the detector and one end of a rod-shaped external connector (11) extending through the housing. A sprung electrical connection is formed.
