Aliexpress
Click here… to search for Xiaomi Mijia Aqara S2 Smart Door Lock on Aliexpress
Here are coupons that you can use.
Latest price update (UTC time):
Banggood
Banggood warehouse is located in China. I am tired of searching coupons, but I found one for you…
Link: Banggood product page
Coupon (253.58 USD): 7bcdf9
(CouponsFromChina.com tip: coupon code has to be applied in shop’s 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): 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
(there’s a little possibility that old coupon will work)
Price history and price alert
Here is price history (for all/most countries) for Xiaomi Mijia Aqara S2 Smart Door Lock.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).