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
Registered jack models require additional power (~6 V AC) for operation of the incandescent dial light. This power is delivered to the telephone set from a transformer by the second wire pair (pins 2 and 5) of the 6P4C connector. RJ21 is a registered jack standard using a modular connector with contacts of up to 50 conductors. It is used to implement a 25-line (or less) telephone connection such as that used in the 1A2 key telephone system. The miniature ribbon connector of this interface is also known as a 50-pin telco connector, CHAMP(AMP), or "Amphenol" connector, the latter being a genericized