Security device monitoring ultrasound emissions in protected space, e.g. car interior

摘要

A sound sensor (1) transmits a sound to an adaptive impedance amplifier (2). The output from the amplifier passes through several low-pass or high-pass filters (3) which select the desired frequency range and its harmonics. A second adaptive impedance amplifier (4) is connected to their outputs prior to an A-to-D converter (5) which allows comparison between the sounds received with those in a memory. The memory contains the characteristic sounds of a break in and if the sounds are identical to those received the normal alarm circuits are set off. An analogue voltage comparator may equally well be used.