Aliexpress
Here are coupons that you can use.
Latest price update (UTC time):
Banggood
Banggood warehouse is located in China. We have found one coupon for this product!
Link: Banggood product page
Coupon (22.09 USD): BGherra
(CouponsFromChina.com tip: paste coupon code in your cart and click Apply after clicking “Proceed to checkout”. Click to copy code and open shop)
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k
Old coupons (from the oldest to the newest): 0e7f33, BGMPB2020, bGhOnEy10
(you can check these old coupons out, but these probably won’t work)
Price history and price alert
Price history (for all/most countries) for WT55 Wall Scanner Wire Detector is here.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).