A piezo electric sounder which can supply levels of over 100 d B at a distance of 30 cm yet is only 4 mm high. It can therefore be used wherever space is at an absolute premium. It requires an external driver which should operate on or as near as possible to the buzzers resonant frequency of 5500 Hz. This source should present a maximum drive voltage of 30 V peak-to-peak to the buzzer. 100 mm lead-out wires with tinned ends are provided. Mounting lugs with 2.5mm holes are moulded into the buzzers cream-coloured case.