Originally Posted by DannoXYZ

Yes! A magnetic field will only induce a current (and resultant back-EMF) when a conductor moves through it. The higher the velocity the higher the induced-voltage. It's like those hand-cranked emergency flashlights; the faster you crank the handle, the more power you generate and the brighter the light. If you creep up to the light very, very slowly, you may never trigger it.

I'll need to look up the amount of induced current in various types of conductors. I suspect CF may not be as good as aluminium, which may not be as good as steel, and copper may be the best. I've found with motorcycles, if you hit the starter button, the EMF from the starter motor is enough to trigger many of these sensors.