According to grocery industry estimates, one US$100 supermarket trolley, or cart, goes walkabout every 90 seconds in the US, theft that is costing retailers millions of dollars a year. Gatekeeper's new device is offering to put a brake on trolley theft, however, by effectively freezing the cart's wheels when it is taken towards a set perimeter of the store. The wheels can only be released by a specially designed 'key'.