Application: for all ages, System: Android 4.3 or later, Net weight: 15g / 0.03lbx, Battery life: 3 months, Battery: button battery CR2032, Color: white + light gray, Protocal range: 10 m reach on doors, Data transmission: Bluetooth 4.0, iOS7 or later, Size: 33.3×33.3×13.2 (mm) /1.31×1.31×0.52 inches.
You can create price alert here, copy coupons and view price history. Let’s see what best price is ATM.
Aliexpress
There’re some similar (or not) items on Aliexpress
You can use link bot to get even lower price:
Click here to search by yourself. Here are coupons that you can use.
Latest coupon code price check (UTC time):
Banggood
Banggood warehouse is located in China. Hmmm… There is no active coupon in Banggood at this moment.
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/i1u
Old coupons (from the oldest to the newest): MISLEEP, vipupgrade8, ML15%Pro, BG18sleepdot, AFfbG10, BGHTSLEE, 0e7f33, FBCOUPON1, BGHOMEA15%, BGAFF10OFF, BGCuponation10, 13f142, BGHONEY2110, BANGGOODSD
(system checks these coupons on every price check (like once per 24 hours), but you can check them out anyway)
Price history and price alert
Here is price history (for all/most countries) for Sleepace Sleep Tracker. The lowest price was: $15.9.
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)).