The "acoustic" or "air" traditional sirens are still in wide use, most notably on North American-type fire apparatus but other countries such as Japan have fitted their apparatus with these types of warning systems as well, as its overtones help the public "locate" and avoid the fire truck—the newer electronic signals disperse almost pure electronic sine wave tones, which are hard to locate, especially in city "canyons" of buildings. Furthermore, "air" sirens are generally much, much louder. In Chile, many vehicles are fitted with three types of audible warnings, which are sounded all at once: the classic "air" siren, the electronic "yelp", and the European two-tone air horns (sometimes newer vehicles are fitted with the electronic version of the latter, commonly called "Hi-Lo").