Indoor localization, or identifying where one is within a building, is a significant challenge. Global Positioning System (GPS) signals usually do not work inside buildings. Not all buildings have Wi-Fi access points, and adding enough access points to be usable for indoor localization is expensive. 

We have developed smartphone applications that can detect changes in magnetic fields caused by doors, walls, and other things inside buildings. The smartphone applications can then use these changes to determine a person's location within a building.