A vibration sensor (500, 800, 900, 1100, 1200, 1700), comprising: a sensor base (520, 820, 920, 1120, 1220) to couple to a vibration source; a piezoelectric transducer (535, 835, 935, 1135, 1235) coupled on a first side of the transducer to the sensor base (520, 820, 920, 1120, 1220); at least one conductor (525, 825, 925) coupled to the piezoelectric transducer (535, 835, 935, 1135, 1235); a seismic weight (510, 810, 910, 1110, 1210) defining a cavity into which the piezoelectric transducer (535, 835, 935, 1135, 1235) is partly disposed such that the seismic weight (510, 810, 910, 1110, 1210) is positioned on a second side of the piezoelectric transducer (535, 835, 935, 1135, 1235); and a compression component arranged to bias the seismic weight (510, 810, 910, 1110, 1210) toward the sensor base (520, 820, 920, 1120, 1220); characterized in that there is a gap between an inner wall defining the cavity of the seismic weight (510, 810, 910, 1110, 1210) and an outer surface of the piezoelectric transducer (535, 835, 935, 1135, 1235); and the sensor base (520, 820, 920, 1120, 1220), the piezoelectric transducer (535, 835, 935, 1135, 1235) and the seismic weight (510, 810, 910, 1110, 1210) are aligned along an axis and arranged so that relative movement between the sensor base (520, 820, 920, 1120, 1220) and the seismic weight arising from the vibration source, including small compressions and bending moments arising from vibrations transmitted through the sensor base (520, 820, 920, 1120, 1220), causes a current to be generated in the piezoelectric transducer (535, 835, 935, 1135, 1235) and an output signal corresponding to the generated current is detectable on the at least one conductor (525, 825, 925). a sensor base (520, 820, 920, 1120, 1220) to couple to a vibration source; a piezoelectric transducer (535, 835, 935, 1135, 1235) coupled on a first side of the transducer to the sensor base (520, 820, 920, 1120, 1220); at least one conductor (525, 825, 925) coupled to the piezoelectric transducer (535, 835, 935, 1135, 1235); a seismic weight (510, 810, 910, 1110, 1210) defining a cavity into which the piezoelectric transducer (535, 835, 935, 1135, 1235) is partly disposed such that the seismic weight (510, 810, 910, 1110, 1210) is positioned on a second side of the piezoelectric transducer (535, 835, 935, 1135, 1235); and a compression component arranged to bias the seismic weight (510, 810, 910, 1110, 1210) toward the sensor base (520, 820, 920, 1120, 1220); characterized in that there is a gap between an inner wall defining the cavity of the seismic weight (510, 810, 910, 1110, 1210) and an outer surface of the piezoelectric transducer (535, 835, 935, 1135, 1235); and the sensor base (520, 820, 920, 1120, 1220), the piezoelectric transducer (535, 835, 935, 1135, 1235) and the seismic weight (510, 810, 910, 1110, 1210) are aligned along an axis and arranged so that relative movement between the sensor base (520, 820, 920, 1120, 1220) and the seismic weight arising from the vibration source, including small compressions and bending moments arising from vibrations transmitted through the sensor base (520, 820, 920, 1120, 1220), causes a current to be generated in the piezoelectric transducer (535, 835, 935, 1135, 1235) and an output signal corresponding to the generated current is detectable on the at least one conductor (525, 825, 925).