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. These acoustic room fingerprints are used to recognize previously-tagged rooms when they are revisited. For comparison, it also shows the position retrieved from Location Services, which determines your coordinates using radio signals from GPS satellites, wifi and cellular base stations. Our experiments have shown that Batphones acoustic method is more accurate than the radio method. 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.