At least if there is a person under age 18 in the vehicle. Effective January 1, 2008, it is unlawful in California for any person in a motor vehicle (whether a driver or passenger) to have in his or her possession, a lighted pipe, cigar, or cigarette, if there is a minor in the vehicle. The law applies whether the vehicle is moving or is at rest. Any person caught violating this law may be punished by fine not to exceed $100. Law enforcement officers are not permitted to stop a motor vehicle for the sole purpose of determining whether a person is in violation of this law. California is actually the third state to ban smoking in cars where minors are present, however, it is the first state to apply the law to all minors under age 18. In 2006, Arkansas and Louisiana both passed similar laws, however, the Arkansas law applies to children up to age 6, and the Louisiana law applies only to children up to age 13.

A 2005 survey found that Californians vastly supported such a law, including 90% of smokers. The legislature recognized that current law, Health and Safety Code section 104495, prohibits smoking within 25 feet of a playground or tot lot sandbox area, and that the new legislation would further protect minors from the harmful effects of secondhand smoke.