when ACtestpen detects voltage, the probe will flash and beep, higher detection voltage, or closer voltage source, higher frequency of dual-range voltage detector. AC Tester detects slow voltage and neutral trigger yellow flash, detects high voltage and live trigger red flash Non: AC circuit tester uses non-method measurement voltage, NCV inductor probe detects AC voltage, you can detect the presence of voltage by simply placing the tip of the circuit tester close to the socket or power cord. The Dual Range Circuit Voltage Tester is a safe double insulation, you don't have to worry about electric shock, the voltage detection tool is very safe, ideal for helping to determine neutral or live and break points Test Dual Range: The current tester detects standard voltage and low voltage range (12-1000VAC/48-1000VAC), making measurements more flexible and accurate. NCV sensitivity is automatically adjusted from low to high, low sensitivity can detect doorbells, thermostats, power strips, etc., high sensitivity is ideal for detection systems such as power supply, using non-wire testers, voltage detection through simultaneous visual and auditory voltage indicators