Taking Steps

Typically, a conventional navigation system helps users locate routes or paths from one location to other locations. However, the conventional navigation systems use maps, streets, and/or a Global Positioning System (GPS) to locate routes or paths. A problem exists with the conventional navigation systems when the user is in a building or other structure, where there are no street identifiers or a map. Another problem may be attributed to a poor or nonexistent connection to GPS satellites due to the user being inside a building or other structure, due to reflection off the exteriors of large buildings or other objects, due to destructive interference of the signals from towers in urban areas, or due to the type of construction materials used in some buildings. These problems make it impossible to rely on the conventional navigation systems to find paths or routes. Thus, when a recorded route or a recorded path is needed later, there would not be one available to help the individual retrace steps.... 

...Techniques for creating breadcrumbs for a trail of activity are described. The trail of activity may be created by recording movement information based on inferred actions of walking, not walking, or changing floor levels. The movement information may be recorded with an accelerometer and a pressure sensor. A representation of a list of breadcrumbs may be visually displayed on a user interface of a mobile device, in a reverse order to retrace steps. In some implementations, a compass may additionally or alternatively be used to collect directional information relative to the earth's magnetic poles.
From: http://www.faqs.org/patents/app/20100318293#ixzz1AcRFamGM