The service also notifies those who are registered via e-mail and text message in case of an emergency as well. All forms of notification involve any necessary steps to take next, including evacuations.
The system can communicate with devices for the deaf and can also narrow down the areas that need to be notified.
The Los Angeles County Board of Supervisors approved the $2 million system in February.
To sign up for the alert program, visit the Los Angeles County Web site.
The Los Angeles Daily News contributed to this report.