According to my DB the lowest price is $14.99 for Wifi Tuya Smart Smoke Detector Sensor (in Banggood). Go down and check coupons out. Remember to check price history if it is available. Let’s see what best price is ATM.
Wifi Tuya Smart Smoke Detector Sensor 80DB Alarm Fire Smoke Detector Wifi Fire Protection Home Security Alarm Smart Life APP
Latest coupon and price update (UTC):
Banggood ($14.99)
Banggood warehouse is located in China. So I have checked for active coupons (all category coupons and old ones), but there was no working coupon in Banggood. Isn’t it too expensive? Hmmm, price is higher than average (which is $12.36 right now), so better set price alert down below…
Link: Banggood product page
Price: $14.99
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k and https://couponsfromchina.com/short/5cd
Old coupons (from the oldest to the newest): BG589b2e
(system checks these coupons on every price check (like once per 24 hours), but you can check them out anyway)
Aliexpress
There’re some similar (or not) items on Aliexpress
Click here to search by yourself. Here are coupons that you can use.
Price history and price alert
Check out price history chart (for all/most countries) for Wifi Tuya Smart Smoke Detector Sensor.
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)).