Aliexpress
Here are coupons that you can use.
Latest coupon and price update (UTC):
Banggood
Banggood warehouse is located in China.
Link: Banggood product page
Coupon (42.39 USD): bgdt15
Coupon (47.69 USD): band10
(CouponsFromChina.com tip: apply code in your basket (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): bgdt98, BGCBDT98, BGvakvaDT, d3ea27, BGAFF10OFF, BGDTNO1, 7d18f7
(you can check these old coupons out, but these probably won’t work)
Price history and price alert
Here is price history (for all/most countries) for DT NO.1 DT98 Smart Watch.
Price records source(s): Gearbest, Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).