musical instruments. They have been prominently featured in works by avant-garde and contemporary classical composers. Examples include Edgard Varèse's compositions Amériques (1918–21, rev. 1927), Hyperprism (1924), and Ionisation (1931); Arseny Avraamov's Symphony of Factory Sirens (1922); George Antheil's Ballet Mécanique (1926); Dimitri Shostakovich's Symphony No. 2 (1927), and Henry Fillmore's "The Klaxon: March of the Automobiles" (1929), which features a klaxophone. In popular music, sirens have been used in The Chemical Brothers' "Song to the Siren" (1992) and in a CBS News 60 Minutes segment played by percussionist Evelyn Glennie. A variation of a siren, played on a keyboard, are the opening notes of the REO Speedwagon song "Ridin' the Storm Out". Some heavy metal bands also use air raid type siren intros at the beginning of their shows. The opening measure of Money City Maniacs 1998 by Canadian band Sloan uses multiple sirens overlapped. Vehicle-mounted Approvals or certifications Governments may have standards for vehicle-mounted sirens. For example, in California, sirens are designated Class A or Class B. A Class A siren is loud enough that it can be mounted nearly anywhere on a vehicle. Class B sirens are not as loud and must be mounted on a plane parallel to the level roadway and parallel to the direction the vehicle travels when driving in a straight line. Sirens must also be approved by local agencies, in some cases. For example, the California Highway Patrol approves specific models for use on emergency vehicles in the state. The approval is important because it ensures the devices perform adequately. Moreover, using unapproved devices could be a factor in determining fault if a collision occurs. The SAE International Emergency Warning Lights and Devices committee oversees the SAE emergency vehicle lighting practices and the siren practice, J1849. This practice was updated through cooperation between the SAE and the National Institute of Standards and Technology. Though this version remains quite similar to the California Title 13 standard for sound output at various angles, this updated practice enables an acoustic laboratory to test a dual speaker siren system for compliant sound output. Best practices Siren speakers, or mechanical sirens, should always be mounted ahead of the passenger compartment. This reduces the noise for occupants and makes two-way radio and mobile telephone audio more intelligible during siren use. It also puts the sound where it will be useful. A 2007 study found passenger compartment sound levels could