Woolworths is trialling new technology that marks shoppers with a digital ID in a bid to curb skyrocketing theft at its stores.

The supermarket chain is using the high-tech system at its Fairfield store in Sydney, with plans to roll it out in other stores across NSW and Victoria.

The technology uses rooftop sensors that identify when someone enters the self-service checkout area and allocates them a unique digital ID.

When the customer has paid for their groceries, a signal is sent to open an exit gate, allowing that person to leave the supermarket.

But if the sensors identify a shopper has not paid - either by pretending to pay or trying to walk straight - the gates will lock closed, preventing their exit.

Woolworths have insisted that the system does not use facial recognition or CCTV so shoppers will remain unidentifiable throughout the process.

The digital ID assigned to each customer is deleted as soon as they leave the store.

A Woolworths spokesperson said the technology was necessary to combat a dramatic rise in theft at its stores.

“We’ve recently begun a trial of new sensor technology at the store to help reduce stock loss and to keep our customers and team safe,” the spokesperson said.

“This is one of a number of initiatives, both covert and overt, to minimise instances of retail crime in store networks across the Group.

“All retailers are experiencing an increase in retail crime, and we’re no exception.

“We continue to look at additional measures that will help reduce retail crime, however, we do understand that most customers do the right thing at the checkout.”