Researchers at Microsoft have created Menlo, a prototype phone that helps you navigate back to a location with "digital breadcrumbs." The phone includes sensors that collects your movements and shows you how to get back to your original location, all without using a GPS.
An accelerometer detects movement, a side-mounted compass determines direction and a barometric pressure sensor tracks changes in altitude.
Menlo includes an app called Greenfield, which leverages the data from the sensors. The goal is to count a user's sequence of steps, gauge direction changes and calculate how many floors the user has traversed by stairs or an elevator. The app stores the trail data so the user can retrace the path.