DO NOT TRY THIS AT HOME OR ANYWHERE
In theory using Faraday's Law of Induction to induce a voltage and current in the coil of wire placed near the high-voltage transmission line. This effect is possible because the alternating current through the transmission line changes the magnetic field around it, and if the inductive coil is positioned so that the magnetic field lines penetrate its area, then an emf will be induced, and an alternating current will flow through the coil.
Too complicated for me! I'll just hope for one from the battery. Usually get 'em when the engine's warm..but for now they're too tight as yet to do it cold. They try, but only do a grunt or two.