As part of the Great California ShakeOut, three counties participated in a test of the emergency alert notification system.Those who live in Yolo, Placer and Sacramento counties and who registered their cellphone numbers, emails and residential landlines should have received a test alert Thursday at 10:17 a.m.“You combine these different tools and these different ways to communicate, and ultimately, through all of those different avenues, you're really trying to achieve that effective communication as best as you can,” said Daniel Bower, director of emergency management in Sacramento. About 430,000 alerts were made to the 160,728 people who signed up for the notifications. “That's a great way to test the system as far as a stress test, and take those analytics and go forward with ways to improve,” Bowers said.But several Sacramento County residents said they didn't get the alerts and had no idea the system even existed.Of the half a million people living in Sacramento, emergency management officials said less than half - only 75,000 people - have chosen to get the alerts. Bowers said the inability to contact everyone is the challenge with an optional system.“I need to reach everybody for an emergency. If they're not signed up, I'm not reaching them,” he said.Many who did receive the alert reported getting the test messages minutes after they were sent. City officials said data is expected in a few days that can give a clearer picture of the reason for the delay. The effectiveness of the test depends on cell tower technology, telecom providers and the alert system itself, officials said. “The last thing that we want to do is pull out this alert system and use it during a time of emergency and time of hazard without actually having some testing done on it,” Bowers said.Sacramento plans to test its system at least once a year.