This early acoustic warning device was from WW1 and still in use at the start of World War Two. This listening device named “Barbier, Bénard and Turenne” was used as an early warning system for incoming airplanes. Used for military and civil protection or with Anti-aircraft batteries as fire guidance. The Germans used them, for example, with 88 mm Flak batteries together with SW 34 Search Lights and these types of acoustic hearing devices to help guide the searchlights and Flak guns.
They became obsolete after the radar came into play, radar was more accurate and had a wider detection range.
