Associated Press -- Some drunken driving offenders will soon have to prove they haven't had a drink before they can start their vehicles.

A law that takes effect today requires offenders to install ignition-interlock devices in their vehicles. If the device detects alcohol on the driver's breath, the vehicle will not start.

The law starts on an experimental basis in four counties - Alameda, Los Angeles, Sacramento and Tulare.

The experiment phase will last five years, after which lawmakers can consider expanding the program statewide.

Supporters hope the built-in Breathalyzers will help reduce accidents and deaths, as they have in other states.