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 (9.99 USD): BGcaa3e6
Coupon (13.80 USD): BG1efeb0
Coupon (13.95 USD): Terence
Coupon (13.95 USD): 2203ActiesNL
Coupon (14.10 USD): BG00c906
(CouponsFromChina.com tip: put item in your cart and apply coupon code there 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): BGOOR3WW, BgcLuBofErtA10, BGZKHDW1, BGTEST37, BGAFF10OFF, BGGDJUT7, BGTESCN02, BGHONEY2110, BGAP2803, BGwhielabel, 13f142, BGAU0407, BG10OFFAFF1, BANGGOODSD, 00c906, ADMITAD2212, BGAlerabat1
(system checks these coupons on every price check (like once per 24 hours), but you can check them out anyway)
Price history and price alert
Check out price history chart (for all/most countries) for Smart Sensor Plant Flower Monitor.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).