ITV News has seen new research showing how customers are cheating at self-checkout machines.
The study which is conducted for retailers is based on 140 million transactions.
It shows how store theft increases when shoppers do their own scanning.
But a new generation of security systems is out to catch the thieves.
The research given to us by ECR Shrinkage Group, a specialist research organisation, shows grocery stores with self-scanning can suffer between 30% and 70% more losses than stores without it.
Watch as a security system flags up a shopper who fails to scan a turkey in her trolley
The study, now being analysed by major retailers, says non-scanning accounts for almost 10% of losses.
Retailers are fighting back with a new generation of self-scan checkouts.
Security features mean colour sensitive software can identify when, for example, carrots are being rung through but steak is being bagged.
Artificial intelligence can take live video monitoring feeds and detect suspicious activity, such as non-swiping.
It seems when it comes to supermarket self-checkouts, some shoppers don't just swipe items themselves - they are helping themselves.