These are sometimes used to test strings of Christmas lights ... We’ve seen various types of non-contact voltage and current sensing over the years. We’ve even seen biological voltmeters ...

Every electrical current generates a magnetic field, so a non-contact voltage tester can detect current in a conductor ...

Non-contact voltage probes have been around a while and some test equipment now has them built-in. This is one of those things that you probably don’t think about much, but surely it isn’t ...