Basically copy coupon, view price history or create e-mail price alert. What is best price?
Standby Time: About 40 days, Resolution: 240*240pixels, APP Name DaFit, Charging Time: About 2.5 hours, Type: TFT, Battery Capacity: 280mAh, Charging Type: Magnetic Charging, Size: 1.3inch, Bluetooth Version BT 5.0, Personalized Watch Face Support, Blood Oxygen Monitor Support, Waterproof 5ATM Waterproof, Using time: About 15 days
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):
Banggood
Banggood warehouse is located in Hong Kong.
Link: Banggood product page
1. ($17.99): BG8a509b
2. ($40.24): BGc70579
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 and https://couponsfromchina.com/short/5cd
Old coupons (from the oldest to the newest): band10, BGWRIBAND10, BGb58412, BG51f436
(sometimes old coupons work, so you can check them out (this site checks them on every price update))
Price history and price alert
Check out price history chart (for all/most countries) for UMIDIGI Uwatch 3S Fitness Tracker.
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)).