(yes, a month old, just got it. --rick)
Courtroom testimony reveals accuracy of SF gunshot sensors a ‘marketing’ ploy
By Jonah Owen Lamb on July 11, 2017 1:00 am
The accuracy of gunshot detection technology used by San Francisco police has
been called into question as part of an attempted murder trial of a man accused
of shooting at a car full of people in 2016.
While the trial of Michael Reed in connection with a shooting on Aug. 13, 2016
specifically focuses on ShotSpotter sensors in the Western Addition, it raises
questions about issues with gunshot detection sensors elsewhere in The City.
Since 2008, the gunshot detection technology has recorded all loud noises and
reported the ones thought to be gunshots to San Francisco police, so they can
Paul Greene, a forensic analyst with ShotSpotter and an expert witness in
Reed’s trial, testified on Thursday in San Francisco Superior Court about the
technology’s accuracy. Manufactured by the company SST in Newark, Calif.,
ShotSpotter guarantees accuracy 80 percent of the time.
In Reed’s case, ShotSpotter failed to pinpoint the exact location of Reed’s
alleged crime near Turk and Buchanan streets, according to Greene’s testimony.
In fact, additional analysis conducted after the shooting, at the behest of
police, determined the location was about a block away from where it was first
“The computer was wrong?” asked Deputy Public Defender Michelle Tong, who is
“Yes,” Greene replied.
In a broader sense, Greene said the gunshot detection system used by the San
Francisco Police Department has not been recalibrated in almost a decade and
that ShotSpotter’s guarantee of accuracy was invented by the company’s sales
and marketing team.
“Our guarantee was put together by our sales and marketing department, not our
engineers,” Greene said.
“We need to give them [customers] a number,” Greene continued. “We have to tell
them something. … It’s not perfect. The dot on the map is simply a starting
The accuracy of the system is significant in Reed’s case because police found
nine shell casings at the scene, while ShotSpotter recorded 11 shots.
Tong contended that Reed fired in self-defense at someone who first fired at
him, hence the extra shots.
However, prosecutor Christopher Ulrich said video and the ShotSpotter
recordings showed Reed firing most of the gunshots, while the extra shots were
fired by a co-defendant, not an enemy.
Despite the testimony, SST’s CEO Ralph Clark said the technology is better than
the guarantee, and SFPD officials were positive about the technology.
The public typically under report gunshots and have little idea where they come
from, according to police.
“This technology pinpoints where [gunfire] is,” Deputy Chief Mikail Ali said.
“If you’re only relying upon the public, we are significantly under reporting.”
Police spokesperson Robert Rueca said officers respond to all ShotSpotter
calls. Still, Rueca would not say how many gunshots are reported each year or
if the department verifies their location accuracy.
“It points in the direction to where we might want to go and investigate,”
ShotSpotter, which the manufacturer claims helps reduce gun violence, can
pinpoint “precise locations for first responders aiding victims, searching for
evidence and interviewing witnesses,” according to SST’s website, which also
noted the technology can report the number of shooters and shots fired.
The company’s technology is used by about 90 law enforcement agencies across
the country, but some departments have decided to axe the service in recent
In 2016, the Charlotte-Mecklenburg Police Department in North Carolina did not
renew its annual contract with ShotSpotter because it failed to help them make
arrests or identify victims.
In 2012, the Detroit Police Department canceled its ShotSpotter contract
because the city had other priorities and not enough officers to respond to
And in 2014, the Oakland Police Department considered ending their contract for
the same reason, but they still use it today.
ShotSpotter was placed in three San Francisco neighborhoods with high crime
rates — Western Addition, Bayview and Mission — in 2008.
In 2010, a grant from the U.S. Department of Justice for $1 million paid to
expand use of the gunshot technology from 3.3 square miles to 4 square miles,
and included new neighborhoods such as Visitacion Valley. It expanded again in
2014 in the Bayview, Western Addition and Mission.
Since fiscal year 2012-13, The City has spent $1.6 million on the ShotSpotter
Neither SST nor police would divulge how many sensors are in San Francisco, but
Clark said there are about 25 per square mile in the outfitted neighborhoods.
For example, during a two-month period in 2009, ShotSpotter recorded 244
gunshots across The City. In 2010, the technology recorded 177 in the same two
The system records all loud noises, Greene said. The computer uses at least
three microphones to locate the gunshot within a 25-meter radius. Then, at
SST’s location in Newark, staff reviews each report to make sure the computer
flags only gunshots.
The two-decade-old company went public June 7 and raised $30 million in NASDAQ
share purchases and had previously raised $67.9 million from 12 venture
But the technology’s accuracy depends on everything from topography,
temperature, humidity and wind speed, as well as the trained ears of employees,
according to Greene.
Clark acknowledged the accuracy of the technology is not perfect, nor is their
guarantee, but he did say it works.
“The 80 percent is basically our subscription warranty, as you will. That
doesn’t really indicate what someone will experience,” he said, adding that it
is usually far better.
Despite changes in topography in the Western Addition, from new buildings to
taller trees, the 46 sensors there have not been retested since they were first
put in, Greene testified last week.
But Clark said the company uses other tools to perfect its system, like
customers who notify them of gunshots that were not reported, which they call
“missed gunshots.” They also keep track of possibly faulty sensors.
Finally, there are false positives, in which there is a gunshot reported with
no evidence of any gunshot.
“We do have a team that analyzes this on a regular basis,” Clark said.
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