The tiny spy

A Dutch acoustics firm, Microflown Technologies, has developed a matchstick-sized sensor that can pinpoint and record a target's conversations from a distance. Known as an acoustic vector sensor, Microflown's sensor measures the movement of air, disturbed by sound waves, to almost instantly locate where a sound originated. It can then identify the noise and, if required, transmit it live to waiting ears. The sensor has no moving parts. It consists of two parallel platinum strips, each just 200 nanometres deep, that are heated to 200°C. Air molecules flowing across the strips cause temperature differences between the pair. Microflown's software counts the air molecules that pass through the gap between the strips to gauge sound intensity: the more air molecules in a sound wave, the louder the sound. At the same time, it analyses the temperature change in the strips to work out the movement of the air and calculate the coordinates of whatever generated the sound.