I WAS recently shopping in Brisbane and visited a supermarket to buy a few groceries. I then proceeded to wheel the trolley out of the shopping centre car park as close as possible to where I lived.
But the wheels locked and I was unable to go further. This occurred at least a couple of times and looking around I realised there were no shopping trolleys outside the shopping centre and all shoppers were replacing theirs in the trolley bays.
The store manager told me that they used a system that magnetised the surrounding parameter of the shopping centre and which automatically locked up the wheels if taken beyond that parameter.