Vehicle horn England, developed a standard electric car horn in 1910. Car horns are usually electric, driven by a flat circular steel diaphragm that has an electromagnet acting on it in one direction and a spring pulling in the opposite direction. The diaphragm is attached to contact points that repeatedly interrupt the current to that electromagnet causing the diaphragm to spring back the other way, which complete the circuit again. This arrangement opens and closes the circuit hundreds of times per second which creates a loud noise like a buzzer or electric bell, which sound enters a horn to be amplified. There
Infrasonic burglar alarm Infrasonic burglar alarm The infrasonic burglar alarm reacts to shock waves in the air that are produced by a break-in. When an intruder tries to break a window or force open a door or a window, the resultant air pressure variations (or shock waves) produce sound vibrations in the air, from 0.1 – 50 Hz. These low frequency sound vibrations are captured by a very sensitive receiver in the alarm and converted into electronic signals. These signals are then passed through a pre-programmed electronic filtering system for analysis and when found positive, activate the alarm siren immediately; thus dissuading the