Humidity range 0%一99%RH, Temperature display resolution 0.1°C, Measure range 0°C-60°C, Executive standard QB/WSDJ 2401-2019, Battery CR2032, Wireless Connection Bluetooth 4.2 BLE, Brand XIAOMI Mijia, Humidity display resolution 1 %RH, Material ABS+PMMA, Quantity 1Pcs, Model LYWSD03MMC, Size 43x43x 12.5mm, Voltage DC2.5V- -3V, CMIT ID 2019DP8115.
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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 and price update (UTC):
Banggood
Banggood warehouse is located in China.
Link: Banggood product page
1. ($18.99): BGTYOI324
2. ($18.99): BGPS324
3. ($25.73): 00c906
put item in your cart and apply coupon code there 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): BGMAYTD324, BGwhielabel, BGYFO24, BGISXIAOMI1, BGSPXIAOMI, BGPT324, BGJUTD324, BGdc324, BGXMFO324, BGPDhome53, BG10OFFAFF1, BGTYOC324, BGTYC324, BGISOC324, BGAUC324, BGAUOC324, BGTYOG324, BGSPHOME41, BANGGOODSD, BGUdb55, BGUbf50
(there’s a little possibility that old coupon will work)
Price history and price alert
Do you need price history chart (for all/most countries) for 4x Xiaomi Smart Bluetooth Thermometer Hygrometer LYWSD03MMC? There we go. The lowest price was: $10.99.
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)).