Tesco is testing whether supermarket customers can buy products without visiting a till.
The UK's biggest retailer has given some staff a smartphone app to use at a store at the company's headquarters.
They use the app to scan barcodes on the products they want and then pay, with no trip to a till needed.
Co-op is experimenting with similar technology and Amazon already has a checkout-free grocery store in Seattle that is open to the public.
Tesco says its experiment is at a very early stage.
It is concerned that checkout-free stores might be a target for shoplifters and, as it operates on very fine profit margins, that could make the technology unviable.
"If the margin in the business is 2 or 3%, you don't have to lose much to make it unprofitable," said chief executive Dave Lewis.
Given Tesco's size, if it did adopt the technology it would be significant advance for checkout-free shopping.
Co-op is also experimenting with a smartphone app that would eliminate the need to visit a till.
It is running a trial at a store in Manchester and will expand those tests over the summer.
However, retail experts are not convinced that grocers can make big savings from the technology.
"Recent stories about the level of theft at self-service checkouts - something that we've had for around 10 years in retail - leaves me to wonder about the obvious savings in checkout-free stores versus a hidden cost in terms of theft," said independent retail analyst Steve Dresser.
"However, you always follow the customer as a retailer. It has always been clear that customers want as little hassle as possible."
Amazon's store in Seattle has a more sophisticated system. Shoppers enter by swiping their smartphone that has the Amazon Go app.
The store uses hundreds of ceiling-mounted cameras and electronic sensors to identify each customer and track the items they select.
Customers can to put any item straight into their shopping bags and purchases are billed to their credit cards when they leave the store.
The Tesco store at its headquarters in Welwyn Garden City is also cashless, which Tesco says has cut the average time spent at a checkout to 45 seconds.
It takes shoppers at similar-sized stores that accept cash an average of 90 seconds at the checkout.