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Wireless Sensors Zero In on Crime

Thirty communities use the ShotSpotter system to identify and locate gunfire and other explosive sounds.
By Claire Swedberg
Aug 22, 2008Last month, the Nassau County Police Department, on New York's Long Island, became the latest in a series of communities and public safety offices to implement the ShotSpotter Gunshot Location System (GLS), a product that uses wireless audio sensors to detect if guns were fired and, if so, calculate the location of those shots. Nassau County police officials deployed the system in Uniondale and Roosevelt, two communities plagued by gun violence.

The system is already in use in about 30 municipalities across the United States. On Dec. 31, 2007, the East Palo Alto Police Department in California completed its own installation of the ShotSpotter. Ten minutes after the system was switched on, it detected gunshots and determined the address of the gunfire, enabling the police officers to quickly find and seize two weapons suspected of being involved. That was the beginning of what has been a successful use of technology to track gunfire in one area of the city, says Captain Carl Estelle. In the past eight months, the system has helped the department make multiple arrests, confiscate guns and nab suspects, Estelle says.

ShotSpotter's Gregg Rowland
ShotSpotter GLS allows government agencies to not only pinpoint the source of a gunshot or explosion, but to use sensor data and auditory recordings for crime-scene investigations (such as searching for spent shells and tire skid marks) and as courtroom evidence. The system's sensors use an IEEE 802.11 protocol to transmit data via signals broadcast at frequency of 900 MHz to 5 GHz.

ShotSpotter Inc. first invented the system about 12 years ago, says Gregg Rowland, the company's senior VP, and spent about six years in further development before marketing it commercially. In 2003 the FBI contacted ShotSpotter for assistance with a Columbus, Ohio, criminal case in which a sniper was shooting at traffic on Interstate 270 around the city.

ShotSpotter provided a server, as well as software to interpret data from sensors, which the company installed in the surrounding area. The system reported the location of subsequent gunshots, helping law enforcement officials to find, apprehend and prosecute the shooter. Since that time, Rowland says, the demand for ShotSpotter GLS has been steady, and a number of major metropolitan areas—including Washington, D.C., Boston, Baton Rouge, La., Philadelphia, Chicago, St. Louis and Glendale, Calif.—now use the system. In addition to the 30 existing systems in operation, he says, the company is installing about one new system each month.

First a ShotSpotter engineer visits the location in which the deployment will take place and uses a spectrum analyzer to sweep the area for RF transmissions, determining which frequency has the least interference. The system sensors are then set to transmit at that frequency.

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