LAS VEGAS (Reuters) - Amazon.com Inc AMZN.O is tracking how regularly customers shop at its store without checkout lines in Seattle, and so far, the verdict is they keep coming back.

FILE PHOTO: A sign for the new Amazon Go store on 7th Avenue at Amazon's Seattle headquarters in Seattle, Washington, U.S., January 29, 2018. REUTERS/Lindsey Wasson

“The ones who work very close, like in the building up above, will come down even just to grab a drink because it’s so fast and easy,” Amazon Vice President Gianna Puerini said in an interview at the ShopTalk e-commerce conference in Las Vegas.

The detail offers an early glimpse at how the store, known as Amazon Go, is faring two months after opening its doors to the public. Shopping frequency, sales and other metrics reviewed by Amazon will likely inform how it thinks about expanding the concept elsewhere in the United States, if at all.

Amazon Go is fashioned after small grocery stores, with a crucial difference: it has no cashiers. Customers scan a smartphone app to enter the store, and then cameras and sensors track what they remove from the shelves and what they put back.

Amazon then bills shoppers’ credit cards on file after they leave.

Puerini said store associates spend the vast majority of their time restocking shelves - another indication of the shop’s popularity.

Research-focused venture capital firm Loup Ventures wrote of Amazon Go last month: “Our experience was flawless, leaving us increasingly confident that Amazon is best positioned to own the operating system of automated retail. Eventually, we expect Amazon to make this technology available to other retailers.”

The world’s biggest online retailer first announced a test of Amazon Go in December 2016, in a challenge to brick-and-mortar rivals that are working to keep their own stores up to date.

However, old practices die hard.

“What we didn’t necessarily expect is how many people would stop at the end, on their first trip or two, and ask, ‘Is it really OK if I just leave?’,” Puerini said.

She declined to discuss specific expansion plans and said there were no plans to add the technology to Whole Foods Market, the upscale grocery chain Amazon bought last year. Analysts have speculated otherwise.

In any case, Amazon is still researching how to improve technology at the store.

“If you show a child a can of Coke, you have to show it to them maybe once or twice, and it’s very easy for them to be able to recognize it,” Amazon Vice President Dilip Kumar said in the same interview with Reuters. “Not so much with computers.”

The company is working to teach computers to recognize items or activities with as little information as possible - a problem that some of Amazon’s thousands of experts are addressing, Kumar said.