I have just checked coupons. The lowest price I could get is $99.99 for Tuya Smart WiFi Home Alarm System Kit (in Banggood). You can create price alert here, copy coupons and view price history. Best price?
Latest coupon and price update (UTC):
Relative humidity: <80%Rh (no condensed), GSM system: 850/900/1800/1900MHz, Reserve battery: 3.7V/500mAh lithium battery, Work temperature: 0 ~ 55 ℃, Alarm number output: <500ma, Working voltage: <120mA, Wireless frequency: 433 MHz, Wireless code: EV1527, The current of the aircraft: <10UA, Input voltage: DC5V (Microusb standard interface power supply), WIFI system: IEEEEE802.11b/g/n wireless standard
Banggood ($99.99)
Banggood warehouse is located in China. I’m afraid that there’s no working coupon in Banggood. Is it expensive? This price is higher than average price ($84.99) for this item.
Link: Banggood product page
Price: $99.99
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k and https://couponsfromchina.com/short/5cd
Old coupons (from the oldest to the newest): BG4e7b81, BGSaleAD, BG92f5fd, BGMARCHSALE, BGAUGUST8, BGCAPITALOS8, BG8FORMULAMX
(you can check these old coupons out, but these probably won’t work)
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
Price history (for all/most countries) for Tuya Smart WiFi Home Alarm System Kit is here.
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)).