1、Electrical On Off Detection: This test pen can test the electrical on off. If the core of the plug is in good condition, the LED green light is on. If it is not on, the core of the plug is disconnected and the contact is not good. 2、Determine Neutral Wire and Live Wire: This test pen can distinguish between the neutral wire and the live wire, insert the electric needle position into the socket, the red and green light works together is the live wire, and plug it into the other socket, the green light is on, it is the neutral wire. 3、Smart Chip: With intelligent motherboard chip, this test pen have enhanced chip control program, making the pen possesses higher security and longer life. 4、Easy Carrying: Comes with small size and lightweight, you can easily take this pen with you to help with your work. 5、ABS Shell: Equipped with ABS shell, this pen is wear resistance, scratch resistance, comes with a long life span. 1 x Test Pen3 x Button Battery Item Type: Test PenMaterial: ABS, 45 SteelLED Lamp Beads: High Brightness Two Color Lamp BeadsMeasuring Range: 70-250VPower Supply Mode: 3 x LR41 Button Battery, Single Battery Capacity 43mAh (Built in Carry Delivery)Backup Battery: 3 x LR41 Button Battery, a Single Battery Capacity of 43mAh (Supporting Delivery)