This is so cool.

"the team has devised a chipless, paper-only version of a radio-frequency identification (RFID) tag. ... [the] design requires no other material than paper. The company simply uses a laser to mark a circuit onto its surface, with the laser settings tuned so as not to cut or burn the paper but to change its chemical composition to make it conductive."

https://www.dezeen.com/2023/10/25/pulpatronics-paper-rfid-tags/