Before Jeffrey Goldstein buys anything while he's in a store, he whips out his smart phone, uses an app to scan the bar code of the item and he comparison shops for the lowest price online.
"I will take a look at everything on the shopping list," said Goldstein.
What he's doing has been dubbed the "scan and scram" or "showrooming," and it's changing the retail landscape.
"This is the new window shopping," said Vipul Lakhi with MyTrioRings.com.
Shoppers are virtually price checking TVs, appliances, clothes and even wedding rings!
"As soon as they find the deal they want, they're ready to jump on it because they've been educated. They're fully aware of what's out there and what they want," said Lakhi.
How many customers are scanning and scramming? One study found that 25 percent of adult cell phone owners used their phones in a store to see where they could buy an item for less. And five percent of those mobile price matchers bought the item online.
Amazon and ebay even launched price comparison apps to make it easier for shoppers.
"It is frustrating to the stores to see this happening," said Klay Huddleston with digital marketing agency Resource Interactive.
It's so frustrating that when the agency went undercover showrooming, one big department store chewed them out. Huddleston says it's time for the big box stores to step up and compete.
"The number of e-commerce sales that were done through this phenomenon, this trend, were large enough that retailers should be paying attention," Huddleston said.
Some traditional retail stores are fighting back through a number of tactics. Target offers exclusive products you can't buy anywhere else. Nordstrom offers free shipping if you buy something in a store or online. Macy's and Old Navy send in-store only coupons. Sears stresses the immediate gratification.
"You can actually get the product the same day you purchase it. No waiting for something to ship to your house, no paying extra shipping charges to get it expedited," said Don Perkins with Sears.
But they'll have to try harder to convince show rooming shopper Jeffrey Goldstein to stop.
"In the big picture, you can save a lot of money," Goldstein said.
Some stores will offer to match the prices of online retailers, so it may be worth showing the manager of the store you're standing in the price comparison you found online and see if they'll give you the same price.