1-2 years ago someone posted here (or on Reddit?) an AQI device with a beautiful UI that was available for purchase for something like $300-400 USD. The onboard display showed a graph of AQI with a small knob to scroll through history. The sensors used were far more sensitive than most consumer products at that pricepoint.

This was something someone had made and was selling through their own site. Anyone remember this? I'm unable to find it.