“I decided to investigate the nightmare DRM RFID chip that was stuck to the bottom of my filter.”
Xiaomi’s 4 Pro purifier reads a password-protected NFC tag on every filter and declares it 0% remaining with about 12 months of life left. Dismiss the warning and it comes back 15 minutes later. A free phone NFC app resets the counter. Xiaomi sells the purifier cheap and the filters forever.