Smog tests, also known as smog checks, are mandatory emissions tests conducted in California to ensure that vehicles meet the state's emission standards. The purpose of these tests is to reduce air pollution and improve air quality. During a smog test, a vehicle's emissions are measured to ensure they comply with the established limits. The specific requirements and procedures for smog tests in California are regulated by the California Air Resources Board (CARB) and the California Bureau of Automotive Repair (BAR). Failing a smog test may result in the need for vehicle repairs or upgrades to bring the vehicle into compliance.