Stephen P. Tarzia

Batphone: Acoustic indoor localization

For my thesis work I developed a set of techniques for determining the location of smartphones while indoors (where GPS is unavailable). I have released an Apple iOS (iPhone, iPod, and iPad) app which demonstrates the technique. It is available for free on the iTunes store.

This work was part of the Empathic Systems project at Northwestern University and is co-authored with Peter A. Dinda (Northwestern), Robert P. Dick (Univ. of Michigan), and Gokhan Memik (Northwestern).

The App

Batphone is a research tool which tests a new method of indoor localization. It uses 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 Batphone’s new acoustic method is more accurate than the radio method. Try it for yourself and let us know what you think!

Batphone does not send any data to us. The only privacy risk for you is that location queries are sent to Apple; this is true of many apps and it can be disabled.

Known issues

These issues may be fixed in a future software release.

  • App will crash on iPod touch (2nd or 3rd generation) if a microphone is not plugged-in.


Version 1.3, released on December 3, 2014, added iOS 7 and 8 support.

Version 1.2, released on July 29, 2011, brought these changes

  • Tweaked UI

  • Fixed accuracy bug on iPhone when Wi-Fi was not enabled

These issues were fixed in the version 1.1 release on January 27, 2011

  • On iPhone 4, app sometimes hangs on the initial "waiting for ten seconds of data..." screen.

Data and Code

The code repository is hosted on github.

Experimental data (recordings) and Matlab code are available here.