![](https://i0.wp.com/www.diymakerdad.com/wp-content/uploads/2021/11/img_3665-scaled.jpg?resize=570%2C350&ssl=1)
This was a little device I built that detected changes in electromagnetic fields. I used it to count the number of cars that drove by a certain spot. The idea was that metal cars would trigger a change in the electromagnetic field, but people and other objects wouldn’t.