Just check coupons out (with price alert and history). Do you want to know what the best price is?
QBKG21LM
Aliexpress
There’re some similar (or not) items on Aliexpress
Click here to search by yourself. Here are coupons that you can use.
Latest coupon code price check (UTC time):
Banggood
Banggood warehouse is located in China. One coupon is available. Cool!
Link: Banggood product page
1. ($28.89): BGSmart6
this code has to be applied in your cart after clicking “Proceed to checkout”. Click to copy code and open shop)
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k and https://couponsfromchina.com/short/5cd
Old coupons (from the oldest to the newest): BGAQAD1S, BgcLuBofErtA10, BG15SH12, BGSTHO15, 13f142, BGHONEY2110, BGSHOM15, BGSHE15, BG0859c9, BGe02387, BGf5d5cc, BGAQA929, BGd324bf, BG10c204, BGD11055, BGB5067, BG479f9e, BG06aabb, ADMITAD2212
(probably won’t work, but you can try them out)
Other warehouses/versions
This item is available in 1 another warehouse/version!
1. Europe – Aqara D1 QBKG24LM Zigbee Smart WIFI Wall Switch [EU] ($-3)
Price history and price alert
Check out price history chart (for all/most countries) for Aqara D1 QBKG21LM Live Line Zigbee Smart WIFI Wall Switch.
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)).