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How the Internet of Things knows where gunfire happens

SST's ShotSpotter pinpoints outdoor, urban gunshots for law enforcement agencies. Now it's moving indoors with a service for schools.

ShotSpotter pinpoints individual gunfire incidents and shows trouble spots for longer-term planning.
ShotSpotter pinpoints individual gunfire incidents and shows trouble spots for longer-term planning. SST

There are amusing ideas for the Internet of Things -- Net-connected houseplants, for example. But lest you think hooking just about everything up to the Internet is silly or sci-fi, consider this more serious example: telling police exactly where in a city somebody has just started shooting.

A company called SST has been doing that with technology called ShotSpotter that spreads an array of computer-powered microphones across a city. They notice the sharp crack of outdoor gunfire, then send the data to a computer that calculates just where the shots were fired based on how long it took the audio signal to reach the microphones.

At the same time, miniaturization means that the Internet of Things is spreading, and that means changes to how we live our increasingly data-infused lives. One example: SST is expanding its services so it can detect not just outdoor shootings, but also indoor incidents so tragically seen at schools in Sandy Hook and Columbine.

"This system is meant to be an automatic fire alarm for active-shooter situations," said SST Chief Executive Ralph Clark.

When the sensors detect gunfire, they send audio data to the company. SST screeners check the data to make sure it really is gunfire then notify police of where the incident occurred. Police usually get the report within 30 to 45 seconds of the incident beginning.

SST staff review recordings of each gunshot report and forward real ones to police, usually in less than a minute.
SST staff review recordings of each gunshot report and forward real ones to police, usually in less than a minute. SST

SST was founded in 1995, close to two decades before the term Internet of Things became the big tech buzzword it is today. SST was ahead of the curve, but the curve is catching up. The changes that make the Internet of Things a real technological trend -- smaller computer chips with lower power consumption and cheaper networking abilities -- also make SST's SecureCampus indoor monitoring service possible.

ShotSpotter only works in outdoor areas where the sound of gunfire isn't muffled by buildings and therefore carries long distances, with 15 or 20 sensors per square mile. But a different approach is needed for SecureCampus. Indoor sensors "need to be low-cost and low-profile," Clark said. And now they are -- small enough to be powered by the Ethernet network cables that also transmit their data to rooftop sensors. Those outdoor sensors monitor for outdoor shots and are equipped with mobile-network uplinks.

That means that in addition to more than 80 cities that use ShotSpotter, one high school and one university so far have signed up for SecureCampus, Clark said.

The Internet of Things is a broad term that began with the idea of scads of sensors connected to the Net -- things like thermometers and air pressure sensors for weather stations, water pressure gauges in municipal water supply pipes, or vehicle detectors at traffic lights and weigh stations. These devices communicate to computers that process the incoming data and take actions accordingly -- thus the term "machine to machine," or M2M, that's closely related to Internet of Things.

But the meaning of the Internet of Things has expanded, encompassing consumer technology like home security systems, smartwatches, smoke detectors, and pet trackers.

Analyst firm Gartner forecast in March that there will be 26 billion devices attached to the Internet of Things by 2020, and those devices will provide the foundation for $300 billion in spending that year. Some of that will be spent on devices, but most will go toward services, Gartner expects.

That's music to the ears of companies like SST as well as AT&T and Verizon, which sell SST access to their mobile networks.

AT&T is a US company, but it's got partnerships with other carriers so its customers can use networks in dozens of countries.

"We have an increasing number of international deployments," said Mike Troiano, vice president of AT&T's Advanced Mobility Solutions group. Companies often put SIM cards in products like cars, tractors, and jet engines, he said. "Whether or not it turns on in the US, it starts sending engine diagnostics or reports what's happening."

AT&T also offers consulting services to those who would link equipment beyond the usual mobile phones to its network, testing products for things like antenna performance and reliability in harsh outdoor conditions.

ShotSpotter's software interface
ShotSpotter's software interface SST

"We have in excess of 17 million wirelessly connected machines on the network," Troiano said, up from 15.2 million a year earlier.

A fraction of those are SST's ShotSpotter microphones. It lists more than 80 cities as customers. Most are in the United States, including Miami, Milwaukee, Boston, Oakland, and Washington, D.C., but some are in other countries, including Rio de Janeiro in Brazil.

At $50,000 to $75,000 per square mile per year, the ShotSpotter service isn't cheap, but better mobile networks and sensor technology have brought costs down from earlier days, Clark said. (The company hasn't revealed pricing for SecureCampus, which it launched only this year.)

SST also has a solar-powered ShotSpotter network atop trees in Kruger National Park in South Africa to help authorities find rhino poaching events by faster means than looking for flocks of vultures. Wilderness areas can be large, but Kruger National Park actually has good mobile network coverage, and fewer microphones are needed for a given area because there aren't buildings to complicate sound travel with reflections.

The outdoor ShotSpotter network filters out false positives like backfiring engines and fireworks, and it sends short audio recordings to people who check to make sure suspected gunfire reports are actual gunfire. The indoor system uses different microphones that just detect a couple of frequencies of sound needed to distinguish gunshots, potentially supplemented with infrared light detectors that can recognize the heat of a muzzle blast.

The technology can't distinguish between types of guns, but it can tell police when automatic-weapon fire is being used and reveal the location of multiple shooters. It'll also reveal how many rounds were fired, Clark said.

ShotSpotter in some US cities observes 10 times as many gunfire incidents as are reported via 911 emergency calls, and it locates them more precisely.
ShotSpotter in some US cities observes 10 times as many gunfire incidents as are reported via 911 emergency calls, and it locates them more precisely. SST

The company keeps track of local statistics that can reveal cities' trouble spots and countrywide statistics that reveal the extent of gunfire in the US.

In 2013, the company logged more than 51,000 rounds of ammunition fired illegally. Its tracking is useful not just because it alerts police rapidly when and where there's gunfire, but also because it finds problems that often go unreported, Clark said. In some areas it monitors, less than 10 percent of gunfire ShotSpotter detects is reported.

For that reason, the company hopes not just law enforcement agencies will be interested in its data, but also research organizations such as the Urban Institute.

"To aggregate that data and analyze it could bring a completely new narrative to gun violence that hadn't been available before," Clark said.