An electric field detector for a heatable windshield includes detector lines which extend around a portion of the perimeter of the windshield between the edge of the windshield's electroconductive coating and the leads to one of the windshield bus bars and are electrically insulated from the coating,...http://www.google.com/patents/US4994650?utm_source=gb-gplus-sharePatent US4994650 - Electric field detector for a heatable windshield
