Coming to a canal near you soon...Asda has taken the wraps off a range of high-tech shopping trolleys which it hopes will stop customers making off with them. The supermarket's new techno trolley cost £2.5m to develop. Stores will be fitted with underground cables that create an invisible perimeter. When a techno-trolley passes through the barrier it receives a signal to stop. The break can then only be released by an authorised Asda porter with a special handset. Supermarkets can face prosecution for allowing trolleys to be abandoned.