Batphone!

Batphone is a research tool which demonstrates a method determining your location within a building. Its meant to be an alternative to GPS or iBeacon, and it works by using the microphone to record room ambience. Try it for yourself and let us know what you think Fore more details, please see the report titled Indoor Localization without Infrastructure using the Acoustic Background Spectrum which was presented at the 2011 MobiSys conference.