Test wires using magnets?

I know this is prob not best place to ask, but u all are very smart.

I was watching the show chop,cut, rebuild with the charger.
There was a guy doing tail lights and I swear to god he tested them using a handheld pen like device, and when he used it the lights would turn on when he touched a wire.
I'm not an electrical engineer, but I know the sell devices that can detect current, is there a device that uses magnetism and can induce an electrical charge?

If so what is it called and where do I buy it?