cernoid-leporidae:

Mostly likely an RFID tag. A simple unpowered device that emits a signal when excited by an external magnetic field.

The fun part is that RFID chips are incredibly easy to break, and incredibly easy to clone/copy. Imagine buying your drink, then intentionally burning out the rfid chip with an extra-strong electromagnetic field and raising a stink because the machine won’t give you what you paid for. Free meal vouchers, maybe? Better yet if you can get behind the counter and burn out the chips on every cup at once.

You could also buy a cup, then scan and clone the RFID tag, and see what kind of system they’re using to keep track of what cups have refills left and which ones don’t. I’d bet money that it wouldn’t be complex or hard to reverse-engineer, and then it’s as simple as spoofing the correct information to the RFID chip reader at the drink dispenser, and you get 8000 refills for the next 99999 hours or whatever.

It’s shitty and dystopian when companies do stuff like this, but fortunately they usually do it in a very stupid way that’s easily exploitable if you have the right know-how and some tools.