You can create price alert here, copy coupons and view price history. What is the best price?
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):
Practical Intelligent Home Appliance with Smartphone Control
Banggood
Banggood warehouse is located in Hong Kong. You can get coupon down below.
Link: Banggood product page
1. ($16.37): Cuponation9
paste coupon code in your cart and click Apply after clicking “Proceed to checkout”. Click to copy code and open shop.
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k and https://couponsfromchina.com/short/5cd
Old coupons (from the oldest to the newest): dcaa7b, bg9xmir, 2019SPEDM, bgssaff9, BGXM9IR, aff7off, BGXMIRD8, BGXMPIR10, BGXMIR99, BGaDmITAd, BGXMIR09, BGIRXM9, BGSENSORPL, bgchinafest, BGBFAFF2019, BGCITYADS2019, bGpAnDacHeCk, BGSSS540, 2020CNY, BGAQ20, BGVDay10%off, BGSAMH, BGBDSRA, bGhOnEy10, BGSM15, 13f142, BGSMOFF, BGSAMRTH, BGELIG0920, BgcLuBofErtA10, BGAFF10OFF, BGXMIRSE, BGSTHO15, BGHONEY2110, BGSHE15, BG628efc, BGCL433, 6GSGIT, BG5207be, BG960575, BGD11042, BGe65c44, BGB5049, BG133a4b, BG9de872, ADMITAD2212, BGSmart6, BGJUNEGSG9, 9OFFSUMMER
(these coupons are old, so probably won’t work)
Other warehouses/versions
This item is available in 1 another warehouse/version!
1. Europe – Xiaomi Human Body Sensor [EU] ($-3)
Price history and price alert
Check out price history chart (for all/most countries) for Xiaomi Human Body Sensor.
Price records source(s): Gearbest, 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)).