You’re walking down the street when a shot rings out. You duck for cover and pull out your smartphone. A map of the neighborhood pops up on the screen with a red arrow pointing in the direction the shot came from.

A team of computer engineers from Vanderbilt University’s Institute of Software Integrated Systems (ISIS) has made such a scenario possible by developing an inexpensive hardware module and related software that can transform an Android smartphone into a simple shooter location system. They described the new system’s capabilities in Philadelphia at a recent conference of the Association for Computing Machinery and the Institute of Electrical and Electronics Engineers.

The U.S. Department of Defense has spent millions during the past decade to develop sophisticated sniper location systems that are installed in military vehicles and require dedicated sensor arrays. Most of these systems take advantage of the fact that all but the lowest-powered firearms produce unique sonic signatures when fired. First 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 shock waves 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.

All but the lowest-powered firearms produce unique sonic signatures when fired. A system that combines sensitive microphones, a precise clock, and an off-the-shelf microprocessor can pinpoint location with remarkable accuracy.

Six years ago the Vanderbilt researchers, headed by Associate Professor of Computer Engineering Akos Ledeczi, PhD’95, developed a system that turns soldiers’ combat helmets into mobile “smart nodes” in a wireless network that can rapidly identify the location of enemy snipers with a surprising degree of accuracy. During the past few years, the ISIS team has adapted its system to work with smartphones.

Like the military version, the smartphone system requires several nodes in order to pinpoint a shooter’s location. As a result, it is best suited for security teams or similar groups. “It would be very valuable for dignitary protection,” says Kenneth Pence, BS’77, MS’03, PhD’05, a retired SWAT officer and associate professor of the practice of engineering management, who participated in the project. “I’d also love to see a version developed for police squad cars.”

In addition to the smartphone, the system includes an external sensor module about the size of a deck of cards that contains the microphones and 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 smartphones then transmit that information to the other modules, allowing them to obtain the origin of a gunshot by triangulation.

The researchers have developed two versions. One uses a single microphone per module, relies on both the muzzle blast and shock wave to determine the shooter location, and requires six modules to obtain accurate locations. The second version uses a slightly larger module with four microphones and relies solely on the shock wave. It requires only two modules to accurately detect the direction a shot comes from, but provides only a rough estimate of the range.

The research was supported by a U.S. Defense Advanced Research Projects Agency grant.

Since its establishment in the School of Engineering in 1998, ISIS has become an internationally recognized science and technology center for both designing and creating physical and computational systems, from small, embedded devices like pacemakers to globally deployed complex systems such as networks of satellites.

Fueling its pioneering research are rapid innovations in information technology that drive enormous changes in science and engineering. This information technology growth has an impact on virtually every system encountered by humans: health care, education, transportation, defense and even the environment.

Read more about ISIS’s smartphone research.

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