By the turn of the 20th Century, motorists could choose from a range of equipment (horns, whistles and bells) to make others aware of their vehicles. Bells were initially the most popular but, in the early 1900s, the bulb horn, which made a more penetrating sound, also became popular. However, by 1910 the increase in vehicle speed led to the need for more effective devices - which could be heard at greater distance (of at least an eighth of a mile) and manufacturers produced more powerful whistles, chimes, sirens and horns – some of which were powered by exhaust gases. Taking the form of a ‘honk’ noise, horns make a distinctive, loud and clear sound to draw attention to (mainly) vehicles - to warn of their approach, presence, or another hazard. There is a legal requirement for some vehicles (mainly, but not exclusively, motorised ones) to have some form of audible warning device. Motorised vehicles have had (and have needed) loud pneumatic or electronic horns for some time but, because they are slower and lack power, bicycles often have either a mechanical bell, or classic bulb horn. In the bulb horn, first introduced in France, squeezing the (rubber) bulb pushes - and then pulls - air past a steel reed at the base of the horn, making it vibrate and produce a note, which is amplified by the funnel shape of the horn to make a louder sound.