Aliexpress
Click here… to search for DIGOO DG-LADA 433MHz Motion Detector 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 (10.19 USD): BGDigoo15%
Coupon (10.99 USD): 13f142
(CouponsFromChina.com tip: 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
Old coupons (from the oldest to the newest): 0404digoo, LADA16, 14LADA, 12LADA, BGCITYADS2019, 2020CNY, BGVDay10%off, BGDG15, BGSAMH, 20%DG422
(I don’t think these’re gonna work, but you can try ’em out anyway)
Price history and price alert
Here is price history (for all/most countries) for DIGOO DG-LADA 433MHz Motion Detector.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).