A free app for Android, by Ewoud Smeur.

The unique Marco Polo app can find the source of any sound. Just press the start button and any sound below 2000 Hz will be pointed out by your phone in real time.

Note that two microphones are required for this app to function and even if your phone has two microphones, it may still not work due to android software constraints.

The app currently supports the following phones:Samsung Galaxy S, S, S, and S seriesHTC DesireHTC One (M7 and M8)

You can check if the app works on your phone by tapping the arrow at the bottom of the screen.