Say you're sitting in a Starbucks and see a teenager who looks just like that picture on the missing-child poster you scanned with your smartphone in Safeway two weeks ago.
But you're not sure, so you whip out your phone and check.
Bingo. It's the girl. You click on the highlighted hotline number, which immediately connects you to the cops, who arrive in two minutes flat.
Forget those old forlorn photos on milk cartons. The latest big thing in the search for missing children are "QR codes," a bar-code-like "quick response" technology that puts missing-kid posters in thousands of people's purses and pockets. After Facebook and Twitter, the codes are the latest tools in the tech and social media box aimed at finding kids who vanish.
The day after 15-year-old Sierra LaMar disappeared on her way to her Morgan Hill, Calif., bus stop three weeks ago, a Santa Clara County sheriff's sergeant called San Jose, Calif.-based Child Quest International, suggesting that a QR code be put on Sierra's missing fliers.
Her friends and family also have been tweeting about candlelight vigils, Facebooking a variety of photos and videos of her and using social media to express sympathy and reach out to volunteer searchers.
Earlier this week, the KlaasKids Foundation encouraged people to swap their Facebook profile pictures with those of Sierra to keep her image in the spotlight in what they called an "online vigil." And volunteers have plastered her missing poster — complete with QR codes — across Northern California.
"The problem is educating the community on what a QR code is," said Child Quest's Anthony Gonzalez. "People who know about it rave about it. Others have never seen it and wonder, "What is this thing on the poster?'"
QR codes are printed squares of jumbled black lines and squiggles. When a smartphone equipped with a free QR code app points the phone's camera at the image, it links directly to a website with more photos of the missing child, information and hotline phone numbers. (Haven't seen a missing poster with the QR code? Go to http://uqr.me/missing-sierra-lamar and snap a photo of the computer screen!)
"It essentially makes the missing poster portable," said Stephen Watkins, a Toronto man who works with Child Quest and modified QR codes that were first developed by Toyota to track car parts.
The idea came to him, he said, when he was at a Walmart and noticed customers passing missing posters, glancing briefly and moving on. He is using QR codes and other social media to continue his search for his own two sons, who in 2009 were taken to Poland by their mother.
To humanize the QR code, like he did with his sons' and Sierra's, he embeds a photograph of the missing child.
Technology has come a long way since the milk carton campaign in the 1980s, devised by the National Center for Missing and Exploited Children. That campaign lasted six months and — despite becoming part of the pop culture of the time — was considered a failure, said the center's Bob Lowery.
"People weren't really paying attention to the images on the milk cartoons," he said. "The only ones paying attention were younger children enjoying their cereal."
When the center opened in 1984, it had a recovery rate of 62 percent for missing children. Now, nearly three decades later, that rate is 98 percent. "It's because of better awareness of missing children and also our ability to connect through social media, Amber alerts and all the tools we have," Lowery said.
Even as media interest fades, Sierra's family and supporters can continue to tweet and retweet and add sympathetic friends to their Facebook accounts to keep the story going. After three weeks, the Santa Clara County Sheriff's Department is still staffing its emergency operations center around the clock, staffing tip lines, putting GPS devices on their searchers, and keeping tabs on Sierra's so-far-dormant Facebook and Twitter accounts.
Robert McConnell, a computer programmer from Macedonia, Ohio, credits Facebook with getting him closer to finding his daughter. Even though he had full custody, he said, his daughter's mother took her to her native Indonesia and never came back.
"I thought my only avenue might be trying to get as many friends as I could in Indonesia on Facebook," he said. "I posted my daughter's pictures and everything and sure enough, about a year ago, I was contacted by a woman who knew her."
But the trail went cold when the mother and daughter, Bianca Damanik, now 9 years old, moved to somewhere near Jakarta.
But McConnell isn't giving up.
"I'm just hoping when she gets old enough," he said, "she'll go out and try to find me."