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. Just check coupons out (with price alert and history). What is 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. I don’t think there is an active coupon right now – at least in my database.
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!
Additional Banggood coupons: first page and second page
Old coupons (from the oldest to the newest): BG4e7b81, BGSaleAD, BG92f5fd, BGMARCHSALE, BGAUGUST8, BGCAPITALOS8, BG8FORMULAMX
(sometimes old coupons work, so you can check them out (this site checks them on every price update))
Price history and price alert
Here is price history (for all/most countries) for Tuya Smart WiFi Home Alarm System Kit. The lowest price was: $84.99.
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)).