Originally Posted by cyccommute

You need to read the posts...particularly CB HI's post and the related links. A magnet on a bike, motorcycle, car, head, etc. do nothing when it comes to inductions coils. Yes, they add mass to a bike but the magnetic field of a permanent magnet...even a very, very massive one that would be too big to carry on a bike...is too weak to have any effect on the induction coil unless it's in direct contact with the wires. Magnetic fields of permanent magnets decrease as a square of distance. This means that if the field has a certain strength at one distance, if you increase the distance from the magnet, the strength of the field is 1/4 as strong.

You can reliably trigger stoplights with induction coils by rolling your wheel directly over the wire buried in the pavement for it's entire length. If the coil is a figure 8 coil, line up on the middle of the figure 8 because the coil is more sensitive due to the two wires overlapping. The trick is to find that wire because they can get buried due to repavement of the road.

It's been my experience that people who say they can't trip the light with a bicycle or motorcycle, don't know how the coils work.