Anybody 18 and over must use a hands-free device to talk on their cell phone while driving, and 16-year-old and 17-year-old drivers are banned from texting or talking.
Headsets, earpieces and other hands-free options are big sellers right now for those who have waited for the last minute.
Washington and California are the latest states to get drivers more focused on the road.
"This will mark new protections for drivers. Not only drivers, but their passengers and everybody who's on the road," said state Senator Gloria Ramos.
Eyewitness News went on a ridealong with the California Highway Patrol and saw a lot of people with earpieces on.
CHP said last year, people talking on their cell phones caused more than 1,000 accidents.
The fine for the first offense is $20, but with fees and penalties, it's actually $76. A second offense is $50, but with fees and penalties, it's $190.
While the new hands-free law does not include texting, drivers may still be fined for distracted driving.