Cameras and sensors were turned on Monday at the intersection of westbound Brittan Avenue and Industrial Road, police said.
Warning notices will be issued for the first 30 days the cameras are in place, but after the trial period violators will be fined.
Signs will be posted to warn drivers of the cameras' presence, police said.
The San Carlos City Council adopted the use of red-light photo enforcement last year in an effort to cut down on collisions and improve safety, police said. The city selected Arizona-based Redflex Traffic Systems, Inc. to install and operate the cameras.
Redflex, which also provides photo enforcement in San Mateo and Menlo Park, reviews photos taken at the intersections before sending them to police. The Police Department then sends a citation to the driver.
Cited drivers can review video footage and photographs of the violations online.