Big Ear of the Law Tames Town’s Gunfire

On New Year’s Eve, certain working-class parts of Redwood City used to sound more like Dodge City. Residents would fire so many weapons as the clock struck midnight that in some years the celebratory gunfire lasted nearly an hour.

Not anymore. This year, police said, there were only about a dozen shots fired. What happened? Well, as you might expect, this city in the heart of Silicon Valley turned to technology to tame its gunslingers.

Using an elaborate computer system and a network of microphones placed on rooftops, police can trace gunshots to the source, often a specific address. Since the system was put in place two years ago, the number of reported gunshots there on New Year’s Eve--or any other time of year--has plummeted.

“We used to get hundreds of calls on New Year’s,” said Ward Hayter, a spokesman for the Redwood City Police Department. “We hardly had any this year.”

The system is the brainchild of Dr. Robert Showen, formerly a researcher at SRI International in Palo Alto, which used to be known as the Stanford Research Institute. Now Showen presides over Trilon Technology, a company he launched to try to sell this system to other police departments nationwide. The company’s Web site is at https://www.shotspotter.com

The ShotSpotter system in Redwood City employs eight microphones positioned over a square-mile area that was once plagued with gunshots. The microphones--hidden on rooftops and telephone poles--are connected through open phone lines to a computer at the police department’s dispatch station.

When a gun is fired, sound waves spread like ripples on a pond. The waves reach the hidden microphones at different times, depending on their distance from the shot. Computers compare these different arrival times to calculate the location of the source, plot it on a grid of the city, and present the information to dispatchers on a computer screen.

“It can tell you whether it was in the frontyard or the backyard,” Showen said.

Armed with a printout, police then visit the address. When confronted, residents typically deny knowing anything about it, but police said they rarely have to visit the same house twice.

Police acknowledge that the information they get from the system doesn’t often lead to arrests. But it can be valuable in investigations to know where a shot came from and, therefore, which homes to visit first. Police also use the system as a deterrent, and they’ve made sure residents know it exists.

Some residents were a little nervous at first that the microphones might pick up more than just gunshots--conversations, for instance. But police and Showen say the devices pick up only extremely loud, explosive sounds.

So far, Redwood City is the only municipality to purchase the system, having paid about $100,000. Showen said other cities could lease the system at a cost of about $2,000 a month for every square mile of coverage.

“Los Angeles,” Showen said, “could really use this system.”