Wireless Technology: ZB 3.0, Size Small Body: 25*10*9mm, Transmission Frequency: 2.4GHz, Size Main Body: 40*25*12mm, Working Voltage: 2.4V-3.3V(CR2032 battery), Transmission Range: Indoor: 10~30m/Outdoor: 30~50m, Working Temperature: ‒20°C ~+60°C; 0%~95%RH.
Price history, coupons and price alert are available on this page. Let’s see what best price is ATM.
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’m afraid that there’s no working coupon 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!
Additional Banggood coupons: first page and second page
Old coupons (from the oldest to the newest): Cuponation9, BG864dcc
(you can check these old coupons out, but these probably won’t work)
Price history and price alert
Check out price history chart (for all/most countries) for MoesHouse Tuya ZB Smart Window Door Sensor. The lowest price was: $6.99.
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)).