You might be thinking of this system used by Ikea. https://youtu.be/JRXdlgBe8wg https://youtu.be/JRXdlgBe8wg https://en.wikipedia.org/wiki/Smarte_Carte https:/

You might be thinking of this system used by Ikea. https://youtu.be/JRXdlgBe8wg https://youtu.be/JRXdlgBe8wg https://en.wikipedia.org/wiki/Smarte_Carte https://en.wikipedia.org/wiki/Smarte_Carte looks like it might be the airport system you have in mind. The usual European shopping cart system works with a coin deposit, chains and mechanical locks on each cart, as described in several other comments.