This is suitable for detecting 100V to 600V AC without requiring physical contact with the conductor.
The presence of any voltage between 100V and 600V AC will generate an audible tone, together with a red visual indication.
The integral self test activates the sensor in the tip of the tester at 50Hz as well as checking the battery and LED. The entire circuit, not just the indicator LED, is therefore tested.
This proves that the unit is fully functional and avoids the need for a separate proving unit.
The only non-contact detectors with a built-in proving device that really proves the entire circuit.