Not to quibble with all the frustrated physicists, but magnets may react to aluminum, copper, kryptonite or unobtanium. Non-ferrous bikes often don't trigger traffic sensors. That's the point of the thread. I'd be thrilled to read about capacitors and floating aluminum disks in a science forum -- heck, I like science -- but that's neither germaine nor interesting to the folks who come to this forum to exhange information about (brace yourself) bicycles.