Aliexpress
Here are coupons that you can use.
Latest price update (UTC time):
Banggood
Banggood warehouse is located in China. So I have checked for active coupons (all category coupons and old ones), but there was no working coupon in Banggood.
Link: Banggood product page
Price: -3 USD
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!
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k
Old coupons (from the oldest to the newest): SUN20, 502C6B, 122280, BGRU202, 9eb9a9, vipupgrade8, 15793f, TTxBG10, BGLIG49, BGissam188, BGss8%hl, AFfbG10, BGNIG134, BGST13, BGSO149, BGBINKUPON202, BGBFAFF2019, BGSSLRA, BGCITYADS2019, bGpAnDacHeCk, BGNS139, BGTY34Y, 0e7f33, BGHOMEG12, BGAFF7OFF, BGAFF10OFF, bGhOnEy10, BGTFD54, BGSOTHING25, BGVVDCF, BGLKZZVVDC16, bgshOOp10, BGHome15%, BGHOMEA15%, BgcLuBofErtA10, BGALIBUYMSS, BGDETD202, BGDEFO202, BGCuponation10, 13f142, BGHONEY2110, BG10OFFAFF, BGwhielabel, BGLIG12, BG10OFFAFF1, BGTYOB202, BGd0b05d
(these coupons are old, so probably won’t work)
Price history and price alert
Here is price history (for all/most countries) for Xiaomi Sunny Smart Sensor Night Light.
Price records source(s): Gearbest, Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).