Clemmons, the University of Denver public policy professor, wrote that “despite its rigorous method, this study echoed the results of many previous studies of gunshot detection technology (GDT) — that it seems to have no effect on serious gun crime.”

Afriyie’s solicitor, Kevin Donoghue, said: “I am really pleased with the court of appeal’s decision in Edwin’s case and that he will now have the opportunity to right this wrong. I hope that if the court finds in Edwin’s favour, the City of London police – and other police forces up and down the country – will respect the decision and re-evaluate culture and training surrounding the use of Taser, particularly against marginalised communities who are disproportionately affected by such draconian uses of force by police officers.”

He added that in both cities, districts that used ShotSpotter saw increases in the collection of ballistic evidence and the recovery of illegal firearms. And while the police in both cities also spent more response time at ShotSpotter locations as opposed to 911 calls, none of this activity led to a reduction in crime.

Rod McCullom is a Chicago-based science journalist and senior contributor to Undark whose work has been published by Scientific American, Nature, The Atlantic, and MIT Technology Review, among other publications.

City officials in Durham voted in March to reject a three-year contract extension for ShotSpotter after an evaluation from the Wilson Center for Science and Justice at Duke University School of Law. The study raised questions about ShotSpotter’s accuracy and impact on crime, even as it found the technology more than doubled the number of gunfire notifications, reduced police response times by more than a minute, and resulted in increased arrests. The study, which was not peer reviewed, concluded that it was unable to determine if the technology had prevented or reduced crime.

“What we found in both cities was that the police response to reports of gunfire seemed to have improved following the installation of ShotSpotter,” Piza told Undark.

But from the beginning, critics have questioned ShotSpotter’s actual impact on handgun violence, its accuracy, and the reliability of SoundThinking’s closely guarded, proprietary data. Now a growing number of cities — including Chicago, believed to be one of ShotSpotter’s largest markets — are having second thoughts or abandoning their commitment to the strategy.

Piza said he was surprised by some of the results. He assumed that there would be a higher clearance rate for shootings. “And we just didn’t find that.”

One notable study of ShotSpotter’s effectiveness in Chicago was conducted by the MacArthur Justice Center at Northwestern Pritzker School of Law, and assessed ShotSpotter dispatches in the city between July 2019 and April 2021. Eighty-nine percent of the notifications did not lead police to evidence of any gun crime. And about 86 percent of notifications led to no criminal charges at all. There were more than 40,000 total unfounded ShotSpotter deployments during that period.

Meanwhile, an audit conducted by the New York City Comptroller in June found that ShotSpotter “is overwhelmingly inaccurate and leads officers to spend hundreds of hours each month investigating nonexistent shots,” according to The New York Times.

That report was not peer reviewed, but two others that were have appeared this year focusing on the ShotSpotter programs in Chicago and Kansas City, both of which launched their programs in 2012.

In late May, the City Council voted to take control of the contracting process for the city’s ShotSpotter system from the mayor’s office, effectively keeping the technology in place until at least November, when the contract is set to expire. But the council also ordered the Chicago Police Department to collect more data on ShotSpotter’s effectiveness before the contract is renewed. “We haven’t seen gun violence go down as a result of this system,” Jessie Fuentes, an alderperson, said during the meeting, according to the Chicago Sun-Times. “We only get reports of the sound detected.”

“The mayor ran on a platform and he believes that he is doing what he should,” Tom Chittum, SoundThinking’s senior vice president of forensic services, said in an interview with Undark. “But I think our view is removing ShotSpotter from Chicago would be a tragic mistake that would just result in more lost lives in a city that’s already suffered too much gun violence.”

He was later charged with failure to provide a sample for analysis. But when the prosecution was ordered by magistrates to provide body-worn camera footage, it dropped the case.

The technology determines the location of the gunfire — usually within several feet — using readings from three or more sensors. Algorithms use the speed of sound to determine the difference in “arrival” times.

Brandon Johnson, who was elected mayor of Chicago in 2023, vowed during his campaign to curb some mass surveillance tools such as speed cameras and gunshot detection technologies. Johnson has described the ShotSpotter system as expensive and ineffective.

“At the end of the day we can’t say with great confidence that there were shootings that were prevented as a result of the ShotSpotter installation,” said Philip Cook, a Duke University economist and criminologist, and author of the study. Even so, he added, “The possibility of taking a minute or two off the response time would mean the difference between life and death for a victim who’s bleeding out on the scene.”

“Without a positive impact on gun violence prevention, the next best benefit we could hope for would be improvements in clearance rates of violent gun crime cases,” wrote Clemmons, who was not involved in either study. “What we still need to know is whether the increased number of guns recovered by police translates into more cases solved and more shooters charged.”

Afriyie, who works for a local authority supporting care leavers, was driving three friends back from a party in east London on 7 April 2018 when he was pulled over by police in the City. Officers told Afriyie they believed he was speeding but he denied this, pointing out that the road had speed bumps. He believes he was singled out because he was a black man driving a Mercedes coupe.

More than seven years ago, when the city of Chicago began its broad deployment of acoustic technology to identify and locate gunfire in high-crime neighborhoods, supporters promoted the system — which uses acoustic sensors, GPS software, and machine learning algorithms to alert the police in real-time — as an effective way to reduce handgun violence.

Researchers and policy analysts like Clemmons emphasize that policing technologies cannot work in a vacuum. “Whether it’s body-worn cameras, CCTV, or an Apple Watch tracking your heart rate, changes in policies, procedures, and — most importantly — practices must accompany any tool in order for it to make a meaningful difference,” she wrote in an email to Undark. “Then the question becomes: if you’re making all of these other changes to the way you’re doing things, what is the value-add of the technology?”

Afriyie said: “This appeal being allowed represents a significant stride towards justice, not only for me but also for individuals who share similar experiences of being disproportionately targeted by the police.”

A black youth worker who was standing with his arms folded when he was shot with a stun gun by officers during a traffic stop has been given permission to appeal over a lost claim for damages against City of London police.

The Kansas City research, which was also led by Piza and published in Criminology & Public Policy, examined about 11,500 gunfire events located by sensors in Kansas City through the end of 2019.

Det Supt Carly Humphreys, the head of professional standards at the City of London police, said: “The City of London police is aware that permission has been granted for an appeal of a civil claim in relation to an incident that took place on 7 April 2018. It would not be appropriate to comment further at this time.”

At that time, more than 90 cities had adopted the technology developed more than 25 years ago by a San Francisco Bay area firm called ShotSpotter. Today, more than 160 cities are using the ShotSpotter technology, according to its parent company, now called SoundThinking.

“Unsolved homicides and non-fatal shootings are exceptionally damaging to public safety and the community’s trust of police,” Ajenai Clemmons, a University of Denver public policy professor whose research focuses on police-community relations, wrote in an email to Undark. “If there are better strategies and tools for solving these cases, then money should be shifted there rather than to a technology that is expensive to install and maintain, whose benefits remain unclear, and whose effects would always need to be paired with changed officer behavior in order to work.”

A statement SoundThinking public relations manager Jerome Filip provided to Undark, which he asked be attributed to the company, described ShotSpotter as a “vital tool in modern policing” that’s designed to supplement the 911 reporting system. “In more than 80% of all shooting incidents, 911 calls do not come in, leaving victims without necessary aid from first responders. ShotSpotter picks up where 911 leaves off, enhancing police response to shooting incidents, aiding in evidence collection, and ultimately saving lives.”

Police breathalysed him but the machine kept registering an inconclusive result. He was asked to put his hands behind his back to be handcuffed and he refused to do so, saying he had done as police had told him when he had stopped blowing into the device.

The ShotSpotter system uses a battery of microphones and sensors installed high above street level to record, identify, and locate the source of potential gunshots. The sensors are usually on rooftops, the sides of buildings, or on top of streetlights or utility poles. They are trained to recognize the two distinctive audio signatures of gunfire. The first is the muzzle blast from the bullet exiting the chamber. The second audio signature is the distinctive waveform.

The incident and the ensuing court case have stayed with Afriyie. He said: “Daily, I find myself reliving the harrowing events and the ongoing struggles in court. The defence barrister’s relentless dismissal of my traumatic experiences adds to the emotional toll. Since the incident in 2018, the absence of justice leaves an open wound, making it challenging to move forward.”

Researchers have reached similar conclusions in several other cities, including Kansas City, Missouri; Portland, Oregon; and Durham, North Carolina, where officials recently voted to end the city’s gunshot detection pilot project.

The appeal argues that the judge was wrong to assess that the use of a Taser weapon on Afriyie was lawful and that police failed to follow the guidance on its use, which insists that it only be used in circumstances that are “proportionate, lawful, accountable and absolutely necessary”.

“Gun violence victimization did not reduce in either Kansas City or Chicago following the installation of ShotSpotter,” said Piza. “We also found that shootings were no more likely to be solved in either Kansas City or Chicago following the installation of ShotSpotter.”

Since then, there has been a steady stream of research into the technology’s effectiveness. According to a 2024 analysis by an interdisciplinary research team at multiple institutions including Northeastern University and the University of Tampa, the system has had “no effect” on both fatal and non-fatal shootings.

Cleveland recently expanded the technology across the entire city, but other cities like Seattle, Washington and Dayton, Ohio have abandoned their programs.

A high court judge ruled in June that officers “honestly believed” shooting Afriyie with the stun gun was necessary because he “was a large and muscular man” who “was clearly very agitated”.

Afriyie’s legal claim did not go into race discrimination but he said before the high court hearing that police in the incident “treated him like a wild animal” and that it would not have happened if he was white.

Officers claimed in statements that Edwin Afriyie had adopted a “fighting stance” before he was hit by the Taser electrical weapon but police body-worn camera footage showed his arms were folded and he was standing at a distance from them.

According to a 2024 analysis by an interdisciplinary research team, gunshot detection technology has had “no effect” on both fatal and non-fatal shootings in Chicago.

In 2017, when Chicago began expanding ShotSpotter into about half of the city’s neighborhoods, mostly in Black and Hispanic communities with higher rates of firearm violence, there were very few independent studies on gunshot detection technology in general and none on Chicago’s s system.

Granting permission to appeal, Lord Justice William Davis wrote that having seen the body-worn footage, he believed an appeal had a real prospect of success, and that there was a “sensible basis for arguing that [the judge] fell into error”. The case is expected to be heard at the court of appeal early in 2024.

While the police in both Chicago and Kansas City spent more response time at ShotSpotter locations as opposed to 911 calls, none of this activity led to a reduction in crime.

Afriyie said the high court judge’s initial assessment that the stun gun shooting was justified was “deeply concerning and disheartening” and underlined “some of the systemic issues within the justice system and the challenges faced by black individuals seeking accountability for unjust actions by law enforcement”.

Other cities, including Houston — the nation’s fourth-largest city — are rethinking the merits of gunfire detection. John Whitmire, the city’s mayor, recently described the technology as a “gimmick” with no impact on the city’s serious gun violence epidemic, according to ABC 13 Houston. The news station found that only 5 percent of ShotSpotter notifications over nearly two years led to an arrest.

The Chicago study, which analyzed about 85,500 gunfire events between January 2008 and December 2019, was led by Eric Piza, a professor of criminology and criminal justice at Northeastern University. It is believed to be part of the largest research project on gunfire detection technology to date. The researchers wanted to determine the impact of gunfire locators on officers’ responses and searches, ballistic, and evidence collection, and on gun violence and crime overall.