BSIDE FWT11 RJ11 RJ45 Wire Tracker (Banggood, Aliexpress: Anti-explosion rating: IP 40, Receiver Battery: 6F22/9V, Distance of emitting signal: about 300m., Altitude: <2000m(meter), maximal 80% relative humidity (non-condensing), Storage temperature: -10~50°C, Emitter Battery: 6F22/9V, maximal 80% relative humidity (non-condensing), Operating temperature: 0°C ~ 40°C (the best price with coupon)).
Basically copy coupon, view price history or create e-mail price alert. Let’s see what best price is ATM.
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. One coupon is available. Cool!
Link: Banggood product page
1. ($26.99): BGGines
apply it in your cart after clicking “Proceed to checkout”. Click to copy code and open shop.
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k and https://couponsfromchina.com/short/feV
Old coupons (from the oldest to the newest): BGFWT11, a62237, 2b2b18, AFfbG10, 502C6B, BG15METER, bGhOnEy10, BGherra, BG428334, 13f142, BG428334CN
(system checks these coupons on every price check (like once per 24 hours), but you can check them out anyway)
Price history and price alert
Here is price history (for all/most countries) for BSIDE FWT11 RJ11 RJ45 Wire Tracker. The lowest price was: $12.98.
Price records source(s): Gearbest, 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)).