Lo and behold! A deal hath arrived: $20.99 (with coupon at Banggood). Updated: 07-01-2026.
ZN-MT22 12-in-1 Air Quality Monitor AQI CO2 CO Formaldehyde TVOC PM2.5 PM10 Temperature Humidity TFT Screen 1200mAh Battery High-Precision Sensors – Black
Banggood warehouse: China.
Price: $20.99
Additional Banggood coupons:
1. First page
2. Second page
Aliexpress
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Price history and price alert
Here is price history (for all/most countries) for ZN-MT22 12-in-1 Air Quality Monitor. The lowest price was: $20.99.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood and Aliexpress (only if product name will be the same as on Banggood and I will post it on social media though, so it’s more like Banggood price alert)).