Aliexpress
Click here… to search for Xiaomi Mijia Aqara S2 Smart Door Lock on Aliexpress
Here are coupons that you can use.
Latest coupon code price check (UTC time):
Banggood
Banggood warehouse is located in China. There is one coupon right now! Check this out.
Link: Banggood product page
Coupon (253.58 USD): 7bcdf9
(CouponsFromChina.com tip: just apply this code in your cart after clicking “Proceed to checkout”. Click to copy code and open shop)
Old coupons (from the oldest to the newest): 0448ec, 69139b, 502C6B, e2bcea, Hardware, TTxBG10, aff7off, bgssaff9, AFfbG10, BGhardware, bghardware, BGaqaras2, BGBFAFF2019, BGCITYADS2019, Wholesale20, BG2020NS, BG4860, BG7589, BGAQA15, bGhOnEy10, BG8883, BGdragonBoat, BGSS10%SW, bgshOOp10, BGHWDEALS, BgoFErTaSchInA10, BgcLuBofErtA10, BGAFF10OFF, BGCuponation10
(sometimes old coupons work, so you can check them out (this site checks them on every price update))
Price history and price alert
Do you need price history chart (for all/most countries) for Xiaomi Mijia Aqara S2 Smart Door Lock? There we go.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).