Is ShotSpotter gunshot detection tech working for Milwaukee?

Since 2010, the city has spent $3.7 million maintaining a ShotSpotter network as gun violence continues to rise

By: - December 8, 2022 7:00 am
The Milwaukee Police Administration Building downtown. (Photo | Isiah Holmes)

The Milwaukee Police Administration Building downtown. (Photo | Isiah Holmes)

Since 2010, technology to detect and locate gunfire called ShotSpotter has steadily expanded in the city of Milwaukee. The network of acoustic sensors, operated jointly by the Milwaukee Police Department (MPD) and the ShotSpotter company, is intended to boost situational awareness and responses by police to gunfire. Milwaukee’s contract with ShotSpotter will expire and require renewal at the end of March 2023. The expiration may also open the door for community members to debate the future of ShotsSpotter in Milwaukee.

A Milwaukee police squad in front of the Municipal Court downtown. (Photo | Isiah Holmes)
A Milwaukee police squad in front of the Municipal Court downtown. (Photo | Isiah Holmes)

Although Milwaukee is ShotSpotter’s only customer in Wisconsin, the technology is utilized in more than 135 cities nationwide. Through a network of acoustic sensors, the technology detects loud impulsive sounds like gunshots, fireworks, and even backfiring cars. Once captured, sounds that are likely not gunfire are dismissed by ShotSpotter’s computer system. Any remaining sounds are immediately forwarded to an acoustic analyst employed by ShotSpotter. Typically within 60 seconds of first detecting a sound, law enforcement are issued a ShotSpotter alert with the time, location, and number of shots fired.

In a statement to Wisconsin Examiner, the company claimed that ShotSpotter “is highly accurate, with a 97% accuracy rate for detections across all police department customers for the last three years, as independently verified by data analytics firm Edgeworth Analytics. We are trusted by police departments in over 135 cities nationwide and have a 99% customer retention rate, indicating that our system works well.” The 2021 Edgeworth study emphasizes that 88% of gunshot incidents go unreported by police. The company touts ShotSpotter as “the first end-to-end precision policing platform,” a trademarked statement.

Community organizers and activists, however, have cast doubt on the effectiveness of ShotSpotter. Jacob Wourms, campaign and research manager for Campaign Zero — a group that works to redefine public safety and supports community solutions that do not involve police violence — is among them. Members of Campaign Zero have filed records requests involving the technology with police departments nationwide. Campaign Zero obtained records from Milwaukee, showing aspects of the contract with ShotSpotter.

A diagram showing how ShotSpotter works. (Screenshot courtesy of ShotSpotter)
A diagram showing how ShotSpotter works. (Screenshot courtesy of ShotSpotter)

In Milwaukee, the group learned that since 2010, the city has spent more than $3.7 million over the course of the ShotSpotter contract. With each passing year, the contract also saw increases in expenses. From April 2017 to March 2018, the costs for maintaining Milwaukee’s ShotSpotter network increased by $315,813. In March of 2019, the costs of maintaining the contract increased again by $467,087.25, followed by a further increase of $1,401,327 in 2020. This final price increase was what brought  the contract’s lifetime expenses to $3.7 million. In 2021, according to a Forbes analysis, 25.4% of Milwaukee’s population lived below the poverty line.


Documents showing Milwaukee PD’s expenses on ShotSpotter since 2010. (Obtained and shared by Campaign Zero)

When the system was first deployed in Milwaukee, it covered two square miles in the northern portions of the city. Two years later in 2012, the system was expanded by one square mile. Then, two years after that in 2014, the system was again expanded, this time by 8.36 square miles. By the end of the second expansion, ShotSpotter was live in both the northern and southern portions of Milwaukee.

ShotSpotter told Wisconsin Examiner that the annual cost changes between 2017 and 2018 were based on prorated fees for a portion of coverage in 2017, resulting in some fees being less than a full 12-month term. “Milwaukee is currently in a three-year contract, where they have been paying the same annual rate for the past three years,” the company said in a statement. “This is set to expire on March 31, 2023. As any business, we reserve the right to apply modest price increases to annual subscription fees to cover cost increases. These price increases typically never exceed more than 5% per year.”

A graphic of the different kinds of sounds that can cause a ShotSpotter alert. (Photo courtsey of CancelShotSpotter and Campaign Zero.)
A graphic of the different kinds of sounds that can cause a ShotSpotter alert. (Photo courtsey of CancelShotSpotter and Campaign Zero.)

The company added that gun violence has been shown to have a $299 billion impact on the U.S. economy, “significantly more than ShotSpotter’s average cost of $7.99 per square mile per hour of coverage,” the company said in a statement.

Wourms applauded the MPD for responding to Campaign Zero’s records requests in a timely manner. Calling the expansions “discouraging” Wourms told Wisconsin Examiner, “to my knowledge there’s not a great deal of causal proof that ShotSpotter’s doing anything to decrease violence in the city.” He added that, “it doesn’t mean that it doesn’t exist. But I have not seen proof that this is having an impact on gun crime in the city. In plain speak, I have not seen the justification for these continued expansions and giving them more, and more money. So again, Milwaukee’s not unique in that unfortunately. But what we do see is a lot of elected officials just renewing and taking the word of the police and not really asking for that substantive proof.”

On its website, ShotSpotter regularly posts examples of places where it says the technology has succeeded. One example is in Chicago, where shootings are down 20% according to an ABC article from October, 2022. The ABC article mentions ShotSpotter’s role in Chicago’s overall crime prevention strategies. In 2021, the Chicago Police Department said it cleared, or arrested suspects, in about half of its homicide cases, representing a near 20-year high. A quarter of those cases, the ABC article reported, did not result in prosecutors bringing charges. The article also highlights how a $1.4 billion investment to revitalize impoverished parts of the community also played a role.

A view of displays in the ShotSpotter software. (Photo coutesy of ShotSpotter)
A view of displays in the ShotSpotter software. (Photo courtesy of ShotSpotter)

The company also highlighted cases in other parts of the country as well. A study conducted by New York University’s Policing Project and a Purdue University social scientist found that police were alerted to four times more gunfire incidents than  before the technology was deployed. The same study found that police beats where ShotSpotter was deployed saw assaults, including gun-related assaults, decline by about 30%. Another 2020 analysis conducted in Oakland, California found that police were able to find and coordinate immediate medical responses to 101 surviving victims.

None of those examples, however, come from Milwaukee. When asked whether it had data specific to Milwaukee that showed the system improved conditions in the city, ShotSpotter directed the Wisconsin Examiner to MPD. When the same question was posed to MPD in April, the department stated it did not have data to show whether ShotSpotter improved things like clearance rates for cases or response time for police. “There is no data available to answer this question,” the department stated, “however, we are immediately alerted by the system and officers may respond faster to an incident where a firearm was discharged.”

a table filled with guns of many types
“Guns” (Forward Ever | CC BY-ND 2.0)

Homicide rates in Milwaukee have risen and fallen over the technology’s 12 operational years. In 2013 Milwaukee County experienced 103 homicides, followed by a drop down to 86 in 2014. The following year there was a jump  to 147 homicides. For nearly five years after that, homicides dropped again until 2020 when they shot to an all-time high. Milwaukee County had 190 homicides in 2020. That number went up in 2021, and is expected to increase again for 2022. The years where homicides declined between  2015-2019 coincided with  a rise in violence prevention organizing among community members.

Wourms emphasizes various disclaimers ShotSpotter has in its service agreement. Page 15 of the document, which Campaign Zero obtained from another police department, outlines a series of disclaimers which conflict with the technology’s self-reported record.


ShotSpotter Respond Services Agreement

A ShotSpotter services agreement, note Pg. 15, Section C. (Obtained and shared by Campaign Zero)

“ShotSpotter does not warrant or represent, expressly or implicity, that the Software or Subscription Services or its use will: result in the prevention of crime, apprehension or conviction of any perpetrator of any crime, or detection of any criminal; prevent any loss, death, injury, or damage to property due to the discharge of a firearm or other weapon; in all cases result in a Reviewed Alert for all firearm discharges within the designated coverage area; or that the ShotSpotter-supplied network will remain in operation at all times or under all conditions.”

The Milwaukee Police Administration Building in downtown Milwaukee. (Photo | Isiah Holmes)
The Milwaukee Police Administration Building in downtown Milwaukee. (Photo | Isiah Holmes)

In a statement to Wisconsin Examiner, ShotSpotter stated that “it is standard for a software vendor to include legal verbiage in their service level agreements to address what its software or services are warranted to do, and are not warranted to do.” The statement continued that, “as such, our contracts reflect that the ShotSpotter is a tool to assist its customers in the detection and location of gunfire; however, ShotSpotter has no control over how, or if, a customer responds to an incident alert. A rapid response to a ShotSpotter alert may help increase the likelihood of earlier transport to a trauma center, assist officers in the collection of evidence, or possibly locating a suspect; but, ShotSpotter cannot warrant or guarantee that the victim will survive, the police will find evidence, a suspect will be found and arrested, or convicted, or that the system will prevent gun crimes from occurring.”

ShotSpotter added that, “the service-level agreement is written to reflect that, by itself, ShotSpotter is not a cure-all, but studies have shown it’s a critical part of a comprehensive gun crime response strategy that saves lives.”

The technology has also been linked to controversy in Milwaukee. In February, TMJ4 reported that ShotSpotter was deployed in predominately African American areas, some of which had fewer gunshot alerts than in more diverse districts.

US map made out of guns gun control NRA
Getty Images

As of Nov. 21 of this year, the MPD has received 14,346 ShotSpotter alerts. The vast majority, or over 12,000, come from the northern areas of the city whereas just over 1,300 come from Milwaukee’s South Side.

In June, the Wisconsin Supreme Court reviewed the case of a Milwaukee man who was frisked by officers following a ShotSpotter alert. Officers responded to the alert after about a minute and encountered the man, who appeared to be walking away. After a search, the man was arrested for being a felon in possession of a firearm. The court’s dilemma was whether the man was actually the one who fired shots and triggered the ShotSpotter, or whether he was searched and arrested just for being nearby. The court ultimately sided with the officers. With Milwaukee PD already facing the fallout of a stop and frisk lawsuit, the case raised questions about how much weight ShotSpotter’s technology should have in a decision by officers to stop and search citizens who happen to be nearby.

Wourms feels that a third party should be able to review ShotSpotter’s data to vet its impact on the community. “What we see currently is a lot of correlation,” Wourms told Wisconsin Examiner. In simple terms, if gun violence declines, is it because of ShotSpotter or is it because of a combination of other strategies and factors including but not limited to ShotSpotter?

In a statement to Wisconsin Examiner, the company said: “ShotSpotter is a proven tool that saves lives and helps law enforcement respond to gunfire incidents with a fast, precise police response. Gun violence is a complex issue and there is no single solution for it. However, studies have shown that ShotSpotter brings significant value.” The company referenced several examples, including one study by Professor Dennis Mares of criminal justice at Southern Illinois University which observed a 46% reduction in serious gun violence as compared to before ShotSpotter was deployed in Cincinnati.

ShotSpotter. (Courtesy of #CancelShotSpotter and Campaign Zero)
ShotSpotter. (Courtesy of #CancelShotSpotter and Campaign Zero)

In its introduction, the study noted that “available evidence on the efficacy of [Acoustic Gunshot Detection Systems] is minimal.” The introduction went onto say, “Ratcliffe et al. (2019) reviewed an acoustic system connected to cameras in Philadelphia and found no impact on crime. Similar results are found by Mares and Blackburn (2012; 2020) for a ShotSpotter system in St. Louis. Lawrence, La Vigne and Thompson (2019), are slightly more positive, and suggest that the benefits of AGDS may outweigh the cost.”

“There’s just a lot of nuance to the conversation,” says Wourms. “That’s what we want, we want to actually find the causation. If it’s decreasing violence, we’ll back off. That’s a goal, that’s the goal we share. And our thing to date is that ShotSpotter’s contract explicitly says that it won’t reduce gun violence, it won’t prevent violence. So the company tells on itself in its contracts.”


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Isiah Holmes
Isiah Holmes

Isiah Holmes is a journalist and videographer, and a lifelong resident of Milwaukee, Wisconsin. His writing has been featured in Urban Milwaukee, Isthmus, Milwaukee Stories, Milwaukee Neighborhood News Services, Pontiac Tribune, the Progressive Magazine, Al Jazeera, and other outlets.