Martinshorn is a registered trademark, originally created in the 1930s as a mechanical siren system that uses compressed air to drive sound through metal trumpets, producing a powerful, trembling tone. The familiar “TA–TÜÜ” sound heard from fire trucks, ambulances, and police cars in Germany is actually defined in the DIN 14610 standard. According to this regulation, the official German emergency signal — known as the Folgetonhorn — must consist of two alternating tones with frequencies between approximately 360 Hz and 630 Hz, separated by a perfect fourth (a frequency ratio of 4:3), the same musical interval often used in fanfares. In common usage, "Martinshorn" refers not only to the original pneumatic version with compressor and metal trumpets still used by fire brigades, but also to modern electronic sirens on most police and ambulance vehicles, which reproduce the same DIN two-tone pattern. The tempo of these electronic sirens can vary — typically faster in cities and slower on highways.