When I was updating this page, then coupon price was $8.99 for ANENG B04 Voltage Tester Pen 2pcs (in Banggood). You can create price alert here, copy coupons and view price history. What is best price?
ANENG B04 Digital Voltage Tester Pen AC Non-contact Induction Test Pencil Voltmeter Power Detector Meter Electrical Screwdriver Indicator – 3
Latest coupon and price update (UTC):
Banggood ($8.99)
Banggood warehouse is located in China. There is no active coupon in my database right now (for Banggood). The question is – is it a good price? Well, this price is higher than average price ($5.97)
Link: Banggood product page
Price: $8.99
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k and https://couponsfromchina.com/short/5cd
Old coupons (from the oldest to the newest): BG20236Tool, BGTOOS729, BGeb7d2b
(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
Click here to search by yourself. Here are coupons that you can use.
Price history and price alert
Price history (for all/most countries) for ANENG B04 Voltage Tester Pen 2pcs is here.
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)).