Just check coupons out (with price alert and history). Let’s see what best price is ATM.
Aliexpress
There’re some similar (or not) items on Aliexpress
Click here to search by yourself. Here are coupons that you can use.
Latest price update (UTC time):
Input: 5 V⎓1 A, Carbon Dioxide Range: 400 ~ 5000 ppm [±(50ppm + 5%)], Temperature Range: -10°C ~ 40°C (±2℃) / 14℉ ~ 104℉ (±3.6℉), Power Supply: Built-in Lithium Battery (2400mAh), Product Size: 98 × 90 × 40 mm, Humidity Range: 20 ~ 80 % RH (±5 % RH), Wireless Connection: Wi-Fi (only for 2.4GHz Wi-Fi network)
Banggood
Banggood warehouse is located in China. CouponsFromChina software could not find any coupon for this product in Banggood.
Link: Banggood product page
Price: $-3
It looks like this item is out of stock in Banggood. If you found it then please send me the link. I will replace it.
Click here to search on Banggood!
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k and https://couponsfromchina.com/short/5cd
Old coupons (from the oldest to the newest): Cuponation9, BG8ReviTrage, BGcoupon8off, BGGutscheine, BG8OFFCOUPON, TTBLACK5, BGecf31f, BGb68b3e
(you can check these old coupons out, but these probably won’t work)
Price history and price alert
Here is price history (for all/most countries) for MoesHouse WiFi Tuya Smart CO2 Detector Temperature Humidity.
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)).