The Unethical Info blog searched the web for a deal on a decent air purifier and the Xiaomi 4 Pro seemed to meet all requirements. The filter size, scheduler and air volume ticked all the boxes.

I set it up and thought nothing of it until last week my room was lit with the ‘0% remaining’ replace filter warning. I had set my unit up to disable the LCD so this was an unwelcome surprise. I dismissed the warning by clicking the user button to dismiss the error and 15 minutes later it lit up my room again…

There was nowhere in the app I could disable the warning, having cleaned the filter several times throughout the year I was sure it had at least another 12 months of life left in it. I decided to investigate the nightmare DRM RFID chip that was stuck to the bottom of my filter.

The post details how work from the community was extended to hack the tag.

Now that we know how it works we can modify/reset our own filters. Not everyone has access to a ~$350 Proxmark so I’ve created instructions for updating your tag with any NFC enabled mobile phone.

A matrix of air purifiers tested is included. Read more here.