Horn

Horn:
A horn (also known as a hooter) is intended to give a danger signal on vehicles such as cars and trucks. The first horns were used on American cars in 1908. Soon after, they were also introduced in the Netherlands.
A horn often produces a monotone sound, but multi-tone horns are also in use. Multi-tone horns are prohibited in the Netherlands. The horn must emit a constant tone. When two horns are mounted side by side, each giving a different sound level (one for high and one for low tones), these horns must switch on and off at exactly the same time, so it still seems like one tone.