shopping carts (simply taiwan 2)
In order to keep carts on supermarket grounds, they are chained together.
To use one, you need to insert a 10NT coin (a coin about the size of a quarter worth about 33 US cents) into the gray device and then the red part of the chain unlocks and lets you pull the cart away.
When you are done using the shopping cart, you can return it to any location that has another "red handle device." Once you plug the red thing back into the gray thing, your money is returned to you.
I suppose this also helps to discourage shopping carts from being left abandoned throughout the parking lot.