$9.99 – ANENG AC28 Digital Display Socket Tester UK US EU Plug Polarity Phase Pheck Detector Voltage Test Multi-function Electroscope – EU Plug (White).
I have just checked coupons. The lowest price I could get is $9.99 for ANENG AC28 Socket Tester (in Banggood). Just check coupons out (with price alert and history). You probably want to know what is the best price?
Latest coupon code price check (UTC time):
Banggood ($9.99)
Banggood warehouse is located in China. So I have checked for active coupons (all category coupons and old ones), but there was no working coupon in Banggood. Is it a low price? Well, this price is higher than average price ($4.78)
Link: Banggood product page
Price: $9.99
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k and https://couponsfromchina.com/short/i1u
Old coupons (from the oldest to the newest): BGHUPX071
(these codes were not working in latest coupon update, but you can check them out anyway)
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.
Price history and price alert
Here is price history (for all/most countries) for ANENG AC28 Socket Tester. The lowest price was: $4.06.
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)).