(Measure Precisely) This electrical voltage tester can detect voltages: 12V-1000V, and distinguishes them into 3 voltage classes. The BIP will alert the sensitivity low, medium or high with different frequency and color difference of LED. (Sound & Light Buzzer) The voltage of the electrical tester is displayed at the screen during testing. If the red LED flashes with alarm in rapid rhythm indicates that the firewire is detected. If the red LED does not flash, it means that the zero line is detected. (Safety) Non-contact testing and the pen body insulated ensures safety. It flashes and beeps when the device is near AC voltage. Voltage can be detected safely. without the help of an electrician or a professional. (Non-Contact Voltage Tester) The insulated casing is The voltage detector ensures safety. It flashes and beeps when voltage tester pen is close to AC voltage. Voltage can be detected safely. without the help of an electrician or a professional.