Locating Shooters--There's an App for That

From the Daily Mail:

An app that can pinpoint a gunman's location simply by analysing the sound and shockwaves from a gunshot have been revealed by US researchers. 

The Android app can show a map of exactly where the gunman is located, and is expected to be developed for military and police use in the war on terror. 

... The system works on the principle that all but the lowest powered firearms produce unique sonic signatures when they are fired.  

First, there is the muzzle blast – an expanding balloon of sound that spreads out from the muzzle each time the rifle is fired.  

Second, bullets travel at supersonic velocities so they produce distinctive shockwaves as they travel.  

As a result, a system that combines an array of sensitive microphones, a precise clock and an off-the-shelf microprocessor can detect these signatures and use them to pinpoint the location from which a shot is fired with remarkable accuracy, the researchers say.

In addition to the smartphone, the system consists of an external sensor module about the size of a deck of cards that contains the microphones and the processing capability required to detect the acoustic signature of gunshots, log their time and send that information to the smartphone by a Bluetooth connection.
The researchers have developed two versions.  

One uses a single microphone per module.

It uses both the muzzle blast and shockwave to determine the shooter location. It requires six modules to obtain accurate locations.

The second version uses a slightly larger module with four microphones and relies solely on the shockwave.

It requires only two modules to accurately detect the direction a shot comes from, however, it only provides a rough estimate of the range.

 Obviously, using a silencer and subsonic ammo would obviate the sound waves needed for detection.