Originally Posted by sggoodri

They can easily be adjusted to detect metal bicycle rims. The closest signal to my house will detect an aluminum bicycle rim, with no other metal, placed over the center wire cut, where the alternating electromagnetic field is strongest. I used a nylon bolt to attach an aluminum rim to a piece of wood in order to test this, and to provide my city's public works department with a compact calibration device for bicycle detection.

http://www.humantransport.org/bicycl...nals/green.htm