Just check coupons out (with price alert and history). Do you want to know what the best price is?
Aliexpress
There’re some similar (or not) items on Aliexpress
Click here to search by yourself. Here are coupons that you can use.
Latest price update (UTC time):
Operating Mode Full Touch Screen, Bluetooth Version BT5.2, Compatible OS Android 6.0 or above; iOS 10.0 or above, APP Name Mi Fitness, Brand Xiaomi, Model S1 Active
Banggood
Banggood warehouse is located in Hong Kong. Too bad there’s no coupon right now in Banggood.
Link: Banggood product page
Price: $-3
It looks like this item is out of stock in Banggood. If you found it then please send me the link. I will replace it.
Click here to search on Banggood!
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k and https://couponsfromchina.com/short/5cd
Old coupons (from the oldest to the newest): BGS1ACT, BGc70579, BGS1ACT2, BG4eddff, BGHOBBY17, BGJPS1AT, BG8a0c47, BGHUXC152, BGDealkal06, BGJP61702, BG6a0c34, BGacef4f, BG1f8881, BG72c255, BGbf11dd, BGBRS1A, BGHU2380, BG9f930a, BG8a367f, BG811b36
(probably won’t work, but you can try them out)
Price history and price alert
Here is price history (for all/most countries) for Xiaomi S1 Active Smart Watch.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood and Aliexpress (only if product name will be the same as on Banggood and I will post it on social media though, so it’s more like Banggood price alert)).