Insert the probe of the tester into power socket or get close to the live wire,when the tester defects AC voltage signal ,the induced voltage signal indicator flashes, according to the detected signal indicator flashes, according to the detected signal strength ,the signal strength indicator will show three kinds of color,green, green + red or red, meanwhile the buzzer makes alarming sounds of different frequencies: When AC voltage signal is detected ,the signal intensitay indicator is green(low); When higher AC voltage signal is detectde, the signal intensity indicator is red(high). Specification: Material: ABS Colour: Black Size Chart: Size: 185X35X28mm/7.28X1.38X1.10inch Package Includes: 1 x AC Voltage Tester 1 x User Manual Note: 1. Please allow slightly error due to manual measurement. 2. Due to the difference between different monitors, the picture may not reflect the actual color of the item. 3. Wish you a wonderful on-line shopping!