Vehicle horn horn. Bicycles often have a classic "bulb horn", operated by squeezing a rubber bulb attached to a metal horn. Squeezing the bulb forces air through a steel reed located in the throat of the horn, making it vibrate, producing a single note. The flaring horn matches the acoustic impedance of the reed to the open air, radiating the sound waves efficiently, making the sound louder. Other types of horns used on bicycles include battery-operated horns (sometimes even car horns on 12-volt circuits are incorporated) and small air horns powered by a small can of compressed gas. Oliver Lucas of Birmingham,
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