You can create price alert here, copy coupons and view price history. Best price?
Bluetooth 4.2 Heart Rate / Sleep Monitor IP68 Waterproof
Aliexpress
There’re some similar (or not) items on Aliexpress
Click here to search by yourself. Here are coupons that you can use.
Latest coupon and price update (UTC):
Banggood
Banggood warehouse is located in China. You can get coupon down below.
Link: Banggood product page
1. ($18.38): BGAFF10OFF
put item in your cart and apply coupon code there 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): 502C6B, pllenovo, TTxBG10, band10, BG03W, 10lenovo, BGHX03, 2019SPEDM, AFfbG10, BGHX03W2, BGBFAFF2019, BGPro19, BGLENOVO20, BGVDay10%off, BGband10
(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 Lenovo Cardio Plus HX03W Smartband.
Price records source(s): Gearbest, 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)).