The author seems to be using the uHoo in home monitor, which is what I have myself. They’re pricey but I’ve been happy with mine for 2 years.

uHoo Smart Air Quality Sensor – 9 in 1 Indoor Air Monitor with Temperature and Humidity Gauge, CO2, Dust (PM2.5), VOC, NO2, Allergen Meter -to Breathe Easy and Boost Health with App https://www.amazon.com/dp/B076PV9X99/ref=cm_sw_r_cp_api_glt_...