Price history, coupons and price alert are available on this page. Let’s see what best price is ATM.
Material: PC V0;, Wi-Fi: IEEE 802.11 b 2.4GHZ;, Quiescent current: ≤ 40 μA;, Not included);, Working Voltage: DC3V (2x 1.5V battery, Battery Model: AAA 1.5V;
Aliexpress
There’re some similar (or not) items on Aliexpress
Click here to search by yourself. Here are coupons that you can use.
Latest price update (UTC time):
Banggood
Banggood warehouse is located in Europe 
. There are no coupons for this product in Banggood. There’s only 1 record in my database, so I have no idea if the price is OK.
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): BGSONOFFDW2, BGSONOFF15, BGELIG0920, BgcLuBofErtA10, BGDW2, BGSONOFF16, BG1674, BGSTHO15, BGHONEY2110, BGSHOM15, BGSHE15, 13f142, 6GSGIT, ADMITAD2212, BGSmart6, MVC8SPRING, pROMo8cuPoN, BGJUNEGSG9, BG15Sonoff, BG8b589f, Cuponation9
(these coupons are old, so probably won’t work)
Other warehouses/versions
This item is available in 1 another warehouse/version!
1. China – SONOFF DW2 Door/Window Sensor ($9.59)
Price history and price alert
Not enough data to show price history chart… $9.99 is the only recorded price. It was not cheaper than that since we have saved it in DB.
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)).