Where there is voltage 30 KV and above there is this phenomenon called corona.The thread title says voltage and current detection. The video only mentions voltage detection. Current detection (unbalanced only) would be possible through conduit or equipment enclosures. Voltage detection would not.
That would be my take on the device.While it's a neat bent on non contact testers, methinks most of us would not trust our lives w/them....~RJ~