How do shopping carts’ wheels lock when they’re taken outside of the vicinity they’re in?

Question

I always walk by this one grocery store and always see shopping carts lined up just before the end of the parking lot as it seems people really think the signs stating the wheels will lock is just to deter you from trying, but how does it work? My only guess would be magnetics but even then I still have no idea how that all works but I find it oddly interesting.

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EDIT: Just to add on, I live in Ontario Canada. Not all businesses have this sort of thing but a lot of the bigger companies do. And yes, they are in fact real, I’ve tried to push one before, those things don’t move AT ALL once they’re across the line! Quite interesting.

In: Technology

Answer 1

There’s a mechanism inside one of the wheels that stops it from turning, usually by sticking a pawl into teeth on the inside of the wheel.

It’s controlled by a very short-range radio. There’s an antenna loop around the parking lot that continuously transmits the lock command. Try to cross it and the wheel locks.

Then you can unlock it with a special key fob.

Same basic idea as in wireless dog collars.