Battery: AAA battery * 3 (not included), Operating humidity: 20%-85%, Color box size: 85x 85x 38MM, Working temperature: 0-40 degrees (32F-104F), Standby time: 1 year, Protocol: IEEE 802.11b/g/n, Product size: 63x 63x 22MM, Weight: 70g, Wireless range: 45m, Storage temperature: 0-90%, Wireless type: 2.4GHz.
Basically copy coupon, view price history or create e-mail price alert. What is best price?
Aliexpress
There’re some similar (or not) items on Aliexpress
You can use link bot to get even lower price:
Click here to search by yourself. Here are coupons that you can use.
Latest coupon and price update (UTC):
Banggood
Banggood warehouse is located in China. I found coupon for you. Check this out.
Link: Banggood product page
1. ($18.23): BG589b2e
just apply this code in your cart after clicking “Proceed to checkout”. Click to copy code and open shop.
Additional Banggood coupons: first page and second page
There were country-specific coupon codes published on Couponsfromchina social channels and price alerts. Coupon price may vary by country, because there’re different VAT rates, shipping cost etc. There is a chance that some latest coupons are still working:
Old coupons (from the oldest to the newest): BG611daf, BG00c906
(probably won’t work, but you can try them out)
Price history and price alert
Check out price history chart (for all/most countries) for Guudgo Tuya WiFi Human Body Sensor. The lowest price was: $7.79.
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)).