They don't require a battery. They don't need to be plugged into anything. You just wave them at a sensor and then you're on your way to pay for goods, travel on a subway, or ride on a bus. NFC cards might appear to work by magic but it's just good old-fashioned electronic engineering. But the scale of what goes on is really incredible, as one distinguished computer scientist discovered.
Processor die images are things of wonder and we've all gazed and wondered at the work of the likes of. This thing is on another level altogether, though. Not because it comprises billions of transistors or because it's made on a cutting-edge process node —it's the fact that you can see the individual transistors making up the logic gates that process the data.
That single wafer will give you over 200,000 usable dies, so NFC card makers are only looking at six cents per die, which will only be a tiny fraction of the manufacturing cost of the entire card. Similar chips, ones with more security features, are used in contactless bank cards, hotel room 'keys', and smartphones of course.