California law requires you to take a breath or blood test if you are arrested for a DUI. California's "implied consent" law says that if you are lawfully arrested by a police officer who has probable cause to believe that you have been driving under the influence, then you consent to take a chemical test of your blood, breath, or urine for the purpose of determining your blood alcohol content (BAC). The test must be taken at the time of your arrest, and the officer should give you the choice between a blood or breath test. If neither blood nor breath tests are available, then you have to take a urine test. Additionally, California's implied consent law says that you consent to take a preliminary breath test, even if you have not been arrested. This works like a field sobriety test. The officer will use the results to establish probable cause that you were driving under the influence. You do not have to take this preliminary test, and the officer should say so. Refusing it, however, probably won't work in your favor if the officer has some other reason to think you had been drinking. Based on that other reason, the officer could still arrest you, and then you will be required to take a blood or another breathing test. Refusing to take the tests will result in a suspension or revocation of your driver's license by the Department of Motor Vehicles.