Post date: Nov 27, 2014 6:1:18 PM
This code uses the magnetometer built in the iPhone to track magnets around the phone with precision. At this time, it doesn't appear to be built into an available app, but the author, Ivo Leko, appears to be offering the code as part of a development library.
https://www.youtube.com/watch?v=fJlgDIO3oL8