Aliexpress
There’re some similar items on Aliexpress in my database. There may be some other items though.
| Image | Product (link) | Price | Coupons |
|---|---|---|---|
 |
4 pcs. Xiaomi Aqara Door Window Sensor | 0.00 USD | – |
 |
4 pcs. Xiaomi Aqara Water Immersing Sensor | 0.00 USD | – |
 |
4 pcs. Xiaomi Aqara Water Immersing Sensor | 0.00 USD | – |
 |
Xiaomi Aqara LLKZMK11LM Two-way Control Module | 42.26 USD | – |
More on Aliexpress…Here are coupons that you can use.
Latest coupon and price update (UTC):
Banggood
Banggood warehouse is located in China.
Link: Banggood product page
Coupon (59.22 USD): BGSTHO15
Coupon (64.67 USD): 7d18f7
(CouponsFromChina.com tip: apply it in your cart after clicking “Proceed to checkout”. Click to copy code and open shop)
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k
Old coupons (from the oldest to the newest): BGAQFEK8, aff7off, BGaDmITAd, BGBFAFF2019, BGCITYADS2019, Email3, BG9NY, 2020CNY, BGAQ20, BGSAMH, BGAQA15, bGhOnEy10, BGSM15, BGSMOFF, bgshOOp10, BGSAMRTH, BGELIG0920, BgcLuBofErtA10, BG15SH12
(I don’t think these’re gonna work, but you can try ’em out anyway)
Price history and price alert
Check out price history chart (for all/most countries) for Xiaomi Aqara Sensor Kit.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).