Receiving Sensitivity: <-98d, Battery size: 16x 32mm, Size: 45x 24x 11.5mm, Working Temp: 0°C to +40°C, Communication Protocol: IEEE 802.15.4 Zigbee 3.0, Battery: CR1632, Max Power: 10dBm, Detection Range: < 20mm. You can create price alert here, copy coupons and view price history. 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 price update (UTC time):
Banggood
Banggood warehouse is located in China.
Link: Banggood product page
1. ($9.34): BGSHOM15
2. ($9.89): BGHONEY2110
3. ($9.99): 13f142
apply it in your cart after clicking “Proceed to checkout”. Click to copy code and open shop.
Additional Banggood coupons: first page and second page
Old coupons (from the oldest to the newest): 2020CNY, BGAQ20, BGHOMEAPP, bGhOnEy10, BGSM15, BGSS10%SW, BGELIG0920, BgcLuBofErtA10, BGAFF10OFF, BGCuponation10, BGb0b38f, BGeb5c7e, ADMITAD2212, BGSmart6, 8Couponsde, MVC8SPRING, 8BGwbg2204, 2203ActiesNL, tRaDetRaCKeR, 8wEbgaInS5, pROMo8cuPoN, BGJUNEGSG9, TTSUMMER8, Cuponation9, BG56d9e6, BG90c71a
(sometimes old coupons work, so you can check them out (this site checks them on every price update))
Other warehouses/versions
This item is available in 1 another warehouse/version!
1. Europe – Xiaomi KONKE Zigbee 3.0 Window Door Sensor [EU] ($-3)
Price history and price alert
Check out price history chart (for all/most countries) for Xiaomi KONKE Zigbee 3.0 Window Door Sensor. The lowest price was: $7.99.
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)).