Real Time Display, Temperature and Humidity Detection, Comfort Level Display, IP45 Waterproof, Features, History Records of MAX/MIN Temperature and Humidity, Power By 1x CR2032 Battery (included), Working voltage 3V, Current 10UA.
Basically copy coupon, view price history or create e-mail price alert. Best price?
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 price update (UTC time):
Banggood
Banggood warehouse is located in China.
Link: Banggood product page
1. ($5.72): BGDigoo15%
2. ($6.06): bGhOnEy10
you should apply the coupon in your cart after clicking “Proceed to checkout”. Click to copy code and open shop.
Additional Banggood coupons: first page and second page
Old coupons (from the oldest to the newest): BC2018, BC333, 484ac6, 502C6B, 0404digoo, e2bcea, vipupgrade8, TTxBG10, AFfbG10, BGBC203, BGBC2033, BGBC2039, BGBFAFF2019, BGBS2038, BGCITYADS2019, BGBFI388, BGBGHFRI15, BGROG215, BG20bc3, BGVDay10%off, BGDG15
(I don’t think these’re gonna work, but you can try ’em out anyway)
Other warehouses/versions
This item is available in 1 another warehouse/version!
1. China – Digoo DG-BC20 IP45 Thermometer Hygrometer White ($-3)
Price history and price alert
Do you need price history chart (for all/most countries) for Digoo DG-BC20 Bathroom Thermometer Hygrometer Black? There we go. The lowest price was: $3.33.
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)).