Most adults will remember the warning system instituted after 9/11, depicting varying threat levels with red, orange, yellow, blue and green lights.
The system didn't last very long because it didn't have much credibility.
On Monday, many of us experienced a jolting new warning. This wasn't related to threats against travelers and American diplomats in North Africa and the Middle East. This was something closer to home — a hunt for the missing children of a murder victim.
All across California, cellphones squawked, even if they were set for silence, to announce an Amber Alert — a notice of a child abduction in rural San Diego County and a description of a car sought by police.
Amber Alerts aren't new. They started in 2002, with media announcements and electronic billboards on state highways. This was the first time California authorities used a new, national system to send a message directly to the vast majority of cellphone owners.
Some people were startled by their screeching phones, others were angry about a late-night wake-up. Some dismissed the alert as a meaningless gesture, another red light-green light warning. Many people said they would opt out of receiving these messages in the future.
And a few calm voices said the alerts would be worthwhile if the system worked just once.
It already has. Twice, in fact.
Not in California; not yet anyway. James Lee DiMaggio is still at large as of this writing, and police are still looking for Hannah Anderson, 16, and, possibly, her brother Ethan, 8.
On July 1, authorities in Cleveland alerted cellphone users to the abduction of an 8-year-old boy. Soon afterward, a man spotted the car described in the alert and called the police, who reunited the child with his mother.
Minneapolis police credit the cellphone system with the arrest of a suspected kidnapper and recovery of an 8-month-old child in February.
These stories add to a history of successes for the Amber Alert system.
In California, 297 alerts were issued via media and electronic billboard between 2002 and this past March, resulting in the recovery of 245 children and the apprehension of 122 suspects, according to the CHP.
The cellphone alert system is managed by the Federal Emergency Management Agency and, besides Amber Alerts, it has been used to deliver warnings about weather — Hurricane Sandy last fall and tornadoes in Oklahoma this year are noteworthy examples.
In California, where scientists are trying to develop an early-warning system for earthquakes, cellphone alerts could give people time to reach a safe place before it's too late.
You might regret missing that warning. Please think twice before opting out.