Barcode? Passé. Here comes the QR.

LOS ANGELES – Suddenly, they're popping up everywhere — those square, futuristic-looking matrixes that appear to be a cross between abstract art and Rorschach tests.

You'll find them in the corner of newspaper and magazine ads, in department store aisles, on product displays, price tags and For Sale signs in front of homes. Giant-size versions have shown up on billboards.

Called quick response codes, or simply QRs, they're the barcode for the digital age — but ones that convey far more information, and which can be scanned by consumers with smartphones and tablet computers to open a Web page, play a video or even place a call.

The technology has been around for years, but only recently has it been embraced by U.S. retailers and other companies looking for fresh ways to connect with customers. The number of QR scans recorded by the industry's leading code maker has soared to 2 million a month, nearly double the rate last year, and up from 80,000 a month in 2009.

"Advertisers are regarding them as the hottest new tool of mobile advertising," said Colin Gibbs, an analyst at research group GigaOm Pro. "They love QRs because they're cheap and easy to deploy, and you can put them anywhere from print ads to the back of stadium seats."

Macy's Inc. has QRs displayed throughout its stores, with signs giving step-by-step instructions on how they're used. Shoppers who aim their smartphones' cameras at the codes get videos — on their phone screens — of makeup guru Bobbi Brown dispensing application tips or Martha Stewart dishing out decorating advice.

Customers at Home Depot get on-the-spot access to how-to guides and videos. Miller Beer put QRs on Lite Beer cans for a summer promotion. Gap Inc., Target Corp., Starbucks Corp. and Ford Motor Co. have used them in advertising.

Real estate company Re/Max International uses QRs to give prospective home buyers information not only about a house, but also neighborhoods and local schools.

QRs were invented in the mid-1990s in Japan, where smartphones gained early acceptance, and where companies such as McDonald's Corp. have long stamped them on hamburger wrappers.

Their widespread adoption in the U.S. has paralleled the growth of smartphones and tablets with high-quality cameras and apps; Nielsen Co. projects that about half of all Americans will own smartphones by year's end.

Consumer awareness still lags behind. Only 5 percent of total smartphone owners in the United States have scanned a QR, according to Forrester Research. But it's on a sharp curve upward. About 25 percent of Android phone owners and 7 percent of iPhone users tried out a QR in the second quarter of 2010, and that number is expected to rise this year, Forrester said.

Still, QRs remain a mystery to many — including some who grew up in the digital age.

Identical twins Matt and Adam Rinne, 32, were puzzling over the squares on a recent afternoon at a Best Buy in Burbank, Calif. Most of the higher-priced gadgets in the store, including laptops and cameras, had codes stamped onto their tags.

"I've seen these things everywhere," said Adam, who like his brother is a personal trainer. "I consider myself somewhat tech savvy, and I still have no idea what they are."

Home Depot, which began putting QRs in stores and on ads in March, is betting that people will soon learn. "This is where other large retailers are heading," said Tom Sweeney, senior director for online strategy at the home improvement chain. "We wanted to make sure we were in line with the retail world. It's definitely coming into its own and becoming a more prevalent way for retailers to connect broadly and engage with customers."

Small businesses have gotten on board as a cost-effective way of marketing to consumers.

Joe's Jeans, a clothing retailer based in Commerce, Calif., will roll out displays with QR codes at its 20 shops in coming weeks. "They'll link to our social media sites, have contact info and eventually product-specific info," said company spokesman Robert Muzingo said.

For privacy advocates, however, QRs are one more source of concern. That's because the codes don't just impart information, they can also collect data on where and when a QR was scanned. They can, in some cases, even latch on to the phone user's name, age and other personal information.

"Theoretically, over time companies can build up their database and amass a collection of information that leads to a profile of who I am and what I buy," said Julie Ask, a mobile marketing analyst at Forrester.

The digital cognoscenti don't appear to be concerned. For now, knowing how to break the QR code is akin to being a member a hip underground club.

Lady Gaga has partnered with Starbucks for a promotion that's triggered by scanning QRs on signs in the coffee shops. Some trendy bars are putting them on drink glasses. Using free sites that generate the codes, some people have put QRs on business cards, which are linked to their Facebook pages, resumes or contact information.

Levi Smith, owner of Jade Monkey Tattoo parlor in Phoenix, has been inking QR codes onto customers since March.

"If I want a tattoo memorial to my family, I don't want to devote a quarter of my body to listing my family members," Smith said. "You can put an incredible amount of information on the QR codes and save space."

Goldilocks bakeries in Southern California offered Easter and Mother's Day cakes this year that came emblazoned with edible QR codes linked to such things as blossoming flowers and a teddy bear that opens and closes its arms.

Still, many do not yet know the QR club's secret handshake.

At the El Capitan Theatre in Hollywood recently, dozens of twenty- and thirtysomethings queued up to see the latest "Pirates of the Caribbean" movie. Placards passed through the crowd urged patrons to scan the large QRs on them. Those who did, they said, would get free popcorn.

No one took out a phone.

One young woman, dressed as a pirate wench, held up one of the placards.

"Uh, what the heck is this?" she asked.