Gunshot detector finally on target

Bugs worked out, system aids police

Lieutenant Harry Cataldo of the Boston police demonstrated how the city's $1.5 million ShotSpotter system works. (Erik Jacobs for The Boston Globe)

At first, Boston's new $1.5 million gunshot detection system had its kinks.

The pizza-size ShotSpotter acoustic sensors, which were placed on rooftops and telephone poles in violence-prone areas, would sound an alarm in heavy rain and misclassify it as firecrackers.

Also, Boston's old brick buildings and narrow streets made it hard for sensors to pick up some gunshots, prompting the head of Silicon Valley-based ShotSpotter Inc. to say last week that Boston has "the hardest acoustics of any city we're deployed in."

But nine months since the city began using the high-tech system, police and the company say they have worked out most of the bugs. Police say the system enables officers to respond to gunfire an average of one or two minutes before someone calls 911, assuming someone does. The 119 sensors have also contributed to 10 arrests.

"It gives us a head start," said Deputy Superintendent John Daley, who oversees the Operations Division where dispatchers use the technology. "Sometimes, 911 calls come in three to five minutes afterward. Sometimes, they don't come in at all."

The sensors, which were placed in a 6.2-mile swath of Dorchester, Mattapan, Roxbury, and the South End, have recorded 642 instances of gunfire this year, roughly three a day, police say.

The Rev. Bruce Wall, pastor of Global Ministries Christian Church in Dorchester, said police appear to be responding faster, cutting gunfire short.

"I will say that people aren't shooting anymore and staying in the area to assassinate people," he said. "They're getting out of the area as fast as they can."

The remaining 29,641 events recorded by the sensors, or 98 percent, have been firecrackers and other loud noises, police say. After spending the first few months dispatching officers to locations where firecrackers were reported, the department has gained enough confidence in the system to ignore most of them.

Typical of the 10 arrests ShotSpotter contributed to was an event the night of May 28. Sensors recorded an 18-year-old male firing a .38-caliber revolver twice near Franklin Park, said a police report. An officer nearby also heard the shots and the suspect or his companion exclaim, "That [epithet] was loud, pow, pow!" The officer arrested the suspect and found the gun in a trash can.

Although 10 arrests might seem underwhelming for the technology championed by Mayor Thomas M. Menino, both police and James Beldock, chief executive of ShotSpotter, say the system improves officers' safety and shortens the search for the source of gunfire.

"There's a knee-jerk reaction when looking at the technology to focus on the arrests, but that's not the real value," Beldock said in a phone interview. His Mountain View, Calif., company has sold the sensors to 30 police departments across the United States, from Oakland, Calif., to Nassau County, N.Y., since 1995. "The primary focus is getting a better picture of what's going on."

Gunshots often go unreported because people are asleep, not around to hear them, or do not want to get involved. Beldock estimated that 70 percent to 80 percent of gunshots in Boston prompt calls to 911, which he said was higher than other cities with ShotSpotter sensors. The figure in Los Angeles, he said, is about 20 percent.

Even if someone calls 911, Beldock said, officers typically respond to the address of the caller, which is not the most reliable way to find the source of gunfire.

ShotSpotter relies on the principle of acoustic triangulation to pinpoint gunshots. Once a loud noise is detected, the equipment calculates the position where the gun was fired and sends the data to computers at police headquarters at 1 Schroeder Plaza.

A green bar turns red on the computer screens of police dispatchers and says whether the noise is a gunshot, a firecracker, a helicopter, or something else. A green sound wave also appears and features a distinctive triangular pattern for gunshots, one that varies if there is more than one firearm.

The screen displays the nearest street address for the gunshot location, the time, and the direction and speed in which the shooter was moving when the shots were fired. Daley said the location is often accurate within several feet.

Lieutenant Harold Cataldo, who runs the ShotSpotter project in Boston, showed a visitor a sound wave from a shooting involving two gunmen firing a half-dozen shots. Once police knew there were two guns, he said, they were able to dispatch extra officers.

As in other cities, some of Boston's sensors are linked to videocameras installed in recent years as another crime-fighting measure, enabling police to hear and see shootings.

ShotSpotter's technology made national headlines in 2003 when federal agents used it to help catch a sniper who had terrorized a stretch of highway in Columbus, Ohio.

Boston's system went online in October. In addition to misclassifying hard rain, the sensors initially had trouble picking up sounds in sections of Dorchester, Daley said. ShotSpotter, which had installed 96 sensors at first, added 23, according to Beldock.

Other cities have experienced similar kinks. The Metropolitan Police in Washington, D.C., had to take its system offline for a few months after installing it in August 2006 because it was so sensitive to loud noises, said Captain Michael Eldridge. In York, Pa., the system has been set off by the home-run cannon at Sovereign Bank Stadium, home of the York Revolution baseball club.

Not everyone in Boston likes the new technology.

The Boston Police Superior Officers Federation filed a complaint with the state Labor Relations Commission in January alleging that ShotSpotter has increased the workload of supervisors of dispatchers, violating the union's contract. The city filed a written response saying the technology makes supervisors' jobs easier.

Menino, for his part, said he is pleased with ShotSpotter and is considering expanding it. "We did have some faults in the original application, but we worked those faults out," he said. "I think it's another tool. It gives us peace of mind in the neighborhoods."

Jonathan Saltzman can be reached at jsaltzman@globe.com.