A gun fires on an Oakland, Calif., street. Residents assume the sound is city din — perhaps a truck backfiring — and ignore it. At the same moment, a sensor-based location system detects the sound and wirelessly transmits it to 911 dispatchers. A software suite identifies it as a gunshot and sends location data to beat officers who deploy to the scene.

Oakland experienced 7599 violent crimes in 2006, which led to the city's dubious distinction as the fourth most dangerous in the U.S. for gun-related violence. The distinction led to the adoption of gunshot-location systems (GLS) that localize gunfire for situational awareness and intelligence gathering, said Oakland Police Department Deputy Chief David Kozicki.

“Frequently, when there are shootings, we don't have citizens immediately calling the police to say someone is shooting a gun,” he said. “[The technology] gives us the ability to start sending police to those areas in advance of calls from the community.”

Gunshot-location systems are fast becoming ubiquitous, as more cities tap into their budgets to invest in the technology for the protection of citizens and public-safety officers alike. For example, ShotSpotter's system not only has been deployed in Oakland, but also in numerous other cities such as Chicago, Minneapolis, Los Angeles, San Francisco and Washington, D.C. Even Newark, N.J. — which has a population of just 274,000 and a median household income which is half that of the state's — spent more than $1.2 million a few months ago to deploy the system in a high-crime area.

The technology has proved its worth. In December 2007, the system alerted Boston police, who ended up saving a 22-year-old man who had been shot in the back and, in a separate case, a woman pregnant with twins who had been shot twice. In addition, in East Palo Alto, Calif., the system contributed to the confiscation by police of a shotgun and a .357-magnum handgun, said Greg Rowland, senior vice president for ShotSpotter.

The GLS system deployed in Oakland operates based on acoustic triangulation. Developed and first deployed in 1995 in Redwood City, Calif., it quickly matured thanks to Moore's Law-level increases in computer processing power, increased GPS accuracy and improved memory storage for graphic engines, Rowland said.

The system relies on GPS technology working in combination with acoustical sensors to pick up the sound waves and locate the muzzle blast. The sensors send acoustic noise to a server installed at 911 or fusion centers to identify the type of gunshot. The server evaluates the information against a database of acoustical fingerprints — noise patterns unique to each object making them. Rowland said the company soon would launch version 6.0, which can determine whether a mortar has been blasted or if an improvised explosive device (IED) has detonated — not just detect gunshots.

Customers determine what the system tracks and how it is displayed on the computer consoles located at the centers or in police vehicles. The technology connects to already-established municipal land-mobile radio networks, or it can be packaged with Cisco, Proxim Wireless and Tropos Networks wireless mesh buildouts, Rowland said.

The cost of the GLS system — assuming that a wireless network already is in place — averages $200,000 per square mile. That's why Oakland's system only covers 7 of the total 56 square miles in the city. Sensors are placed in areas where there is the highest frequency of gun-related violence, Kozicki said.

He added that the system can determine how many shots were fired, whether the perpetrator was on the move or stationary, and the direction of movement — for example, during a drive-by shooting. Best of all, it acts as a force multiplier, helping the Oakland Police Department deal with personnel and resource shortages.

Indeed, the department didn't have the budget to invest in the mobile version of the technology, which wirelessly streams data directly to in-vehicle computers instead of routing the information through 911 centers to officers in the field. The department plans to implement the mobile version when funds are available, Kozicki said.

Urban police aren't the only ones deploying gunshot-location systems. Warfighters also depend on such technology to stave off sniper fire, said Wayne Lundeberg, chief operating officer of Safety Dynamics. The company offers SENTRI, a battlefield-tailored acoustic recognition system that operates based on neurobiological principles — the brain's ability to recognize and discern acoustic signals in high-noise environments.

“It is a network designed to work and think like the human brain,” Lundeberg said. “It can decipher different sounds, from an airplane to a gunshot. There's no limit to the number of the sounds that we can train into the system.”

Multiple microphones collect sound and feed the data to a computer inside a mobile or fixed enclosure. The software suite analyzes the sound and is able to not only recognize small arms and assault rifle fire but also to differentiate it from other battlefield noise, such as rocket-propelled grenades, IEDs and mortar fire.

“There's not a weapon system that we've found — besides silenced weapons — that we can't pick up,” Lundeberg said.

When the system identifies gunshots, it also captures elevation — down to a specific floor in a building — and location, accurate to within 1° longitude and latitude, Lundeberg said. Additionally, it controls video surveillance cameras to the point of automatically moving the viewfinder to capture the gunshot source and then transmitting the video to a command center or first-responder in-vehicle computer; when the video arrives, the server software triggers an audible alarm.

The data can be sent through wired or wireless systems. “[SENTRI] is connected to [user] systems over a straight Ethernet serial line, whether it's wired, wireless, fiber optic or microwave,” Lundeberg said.

Jay Chang and Myron Hohil test vendor systems like the SENTRI, adapt such technologies to meet battlefield specifications and develop in-house technologies. They share the title of branch chief at the U.S. Army's acoustic and network sensors division at Picatinny Arsenal, N.J.

The 6500-acre arsenal is where gunshot-location systems are tested and developed. Most tested technologies can be used in mobile applications by mounting them in vehicles, or in fixed applications by removing the device from the vehicle and installing it in a building such as a security checkpoint. Scout vehicles and Humvees currently are armed with GLS systems that often are removed for deployment at security checkpoints, Hohil said.

Approved systems are required to identify the location, direction, range, elevation and angle of sniper fire. Although Hohil couldn't divulge approved systems that currently are operational or their specifications due to national security concerns, he did say field-deployed localizers can detect gunshots from hundreds of meters away.

Chang is overseeing the development of soldier-wearable GLS sensors that combine Army-developed and off-the-shelf technologies. The requirements for the soldier-wearable system — which is still in an early research phase — are less stringent compared with those of the aforementioned in-vehicle and fixed systems, as they must identify only the direction and range of captured gunshots.

Chang noted that neither the soldier-wearable nor the mobile/fixed units being tested by the Army currently transmit data wirelessly because of the interference encountered by soldiers on the battlefield caused by jamming activities.

According to Chang, adding wireless GLS sensors to an already dysfunctional system doesn't make sense. In addition, powering wireless systems is a challenge on a battlefield. “If you add a radio into a sensor, you require more power; the charge will increase as well as the weight of the sensor,” Chang said. “Those are big issues. Technologically it's possible. As far as application, it's not desired.”

That's not to say it won't happen in the future. “That is where Army R&D is now focusing — wireless communications,” Chang said.