Aliexpress
Here are coupons that you can use.
Other warehouses/versions
This item is available in 2 another warehouse/versions!
1. China – Digoo 433MHz Window Door Sensor (-3 USD)
2. China – Digoo Wired Alert Siren (-3 USD)
Latest price update (UTC time):
Banggood
Banggood warehouse is located in China. Well, there is one coupon available right now.
Link: Banggood product page
Coupon (7.64 USD): BGSmart6
(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): aff7off, BGaDmITAd, bgchinafest, BGDGHO2, BGBFAFF2019, BGCITYADS2019, BGDigoo15%, BGDG15, BGSAMH, 20%DG422, BGSM15, BGSMOFF, BGDGASG, BGSAMRTH, BGDGDSK, BgcLuBofErtA10, BGDGKITG, BG15SH12, BGSTHO15, BGHONEY2110, BG50389f, BG857fd7, BGSHOM15, 13f142, BGSHE15, BGea70c3, 6GSGIT, BG4a7a54, BGa9f19c, BG79c780, ADMITAD2212, MVC8SPRING, 8BGwbg2204, 2203ActiesNL, BG8206c1, tRaDetRaCKeR, 8wEbgaInS5, pROMo8cuPoN, BGJUNEGSG9, Cuponation9, 9OFFSUMMER
(probably won’t work, but you can try them out)
Other warehouses/versions
This item is available in 2 another warehouse/versions!
1. China – Digoo 433MHz Window Door Sensor (-3 USD)
2. China – Digoo Wired Alert Siren (-3 USD)
Price history and price alert
Here is price history (for all/most countries) for Digoo 433MHz DoorBell Button.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).