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,
Personal alarm attention must be given to the fact that these devices can give a 'false sense of security' and therefore place the individual in danger. Some personal safety apps emit a loud intermittent "shrill whistle", in the manner of a personal alarm. According to the Suzy Lamplugh Trust, the best way to use a personal alarm is to activate it, to drop it on the floor near the assailant, and then to immediately run away. Personal alarm A personal alarm is a small hand-held electronic device with the functionality to emit a loud siren-like alarming sound. It is activated either by