If you were out on the street and suddenly heard sniper fire, you would no doubt react by ducking for cover. The problem is, it’s not always obvious which direction the sound is coming from – crouching behind a certain object might shield you from the bullets, but it also might display you nicely in the shooter’s crosshairs. That’s why a team of computer engineers from Nashville’s Vanderbilt University have developed a smartphone-based system, that determines the location at which the gunshots originated.

The system is based on one developed six years ago, by a team led by Prof. Akos Ledeczi. In that setup, microphone-equipped modules located in the helmets of several soldiers work together to create a linked wireless network.

Each module registers the initial muzzle blast of a shot, followed by the shockwaves that the bullet creates as it travels through the air. A central microprocessor uses a highly-precise clock to compare the times at which the various microphones register those sounds. By doing so, and by knowing the location of each of the modules, it can triangulate the approximate location of the shooter.

Ledeczi and company’s new system works in the same way, except instead of modules mounted on army helmets, it utilizes modules mounted on smartphones. Because multiple phones are required, the system is intended for use by groups such as security teams or police forces.

Each module is “about the size of a deck of cards” and contains microphones, along with the electronics necessary to process the gunshot audio, log its time, and then relay that data to the phone via Bluetooth. The group members’ phones then communicate with one another, comparing the times at which they registered the shots, and thus determining the whereabouts of the sniper.

In fact, there are two versions of the new system. One of those requires at least six modules, each one equipped with a single microphone. Using both the muzzle blast and shock wave data, it is able to fairly accurately determine a location. The other version only requires two modules, each one sporting four microphones. It uses just the muzzle blast audio, although it also only provides a rough estimate of location.