Check coupons or create price alert down below. You probably want to know what is the best price?
Wireless connection: Bluetooth 5.0 version, Product size: ①96x40mm (Including mounting plate), Product model: JTYJ-GD-03MI/BB, Product net weight: 139g (including mounting plate and battery), Battery type: CR17450 lithium ytterbium battery, Working humidity: W95%RH (non-condensing), Battery capacity: 2400mAh, Alarm sound: > 80dB (3m directly in front), Working temperature: -10 °C~55 ℃, CMIIT ID: 2020DP15509, Battery life: 5 years (may vary slightly due to different usage environments), Executive standard: GB 2051 7-2006
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. I’m afraid that there’s no working coupon in Banggood.
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/5cd
Old coupons (from the oldest to the newest): BGHONEY2110, BGeb45e9, BGSHOM15, 13f142, BGSHE15, BGCNXMSMK, BG10OFFAFF1, 6GSGIT, BGee66bc, BG6b8458, BG4a7a54, BGB5054, BG69b856, BGc838e9, ADMITAD2212, BGSmart6, MVC8SPRING, 8BGwbg2204
(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 Xiaomi Mijia Honeywell Fire Alarm Detector JTYJ-GD-03MI/BB.
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)).