AI Gunshot Detection (ShotSpotter)

ShotSpotter places acoustic sensors across a coverage area, listens for sounds consistent with gunfire, and alerts police to a location within seconds. Sounds flagged by the algorithm are reviewed by a human analyst at a company review centre before an alert reaches a police department. The company rebranded from ShotSpotter to SoundThinking in 2023; the product name remains.

The premise is intuitive and worth stating fairly: gunfire is substantially underreported to emergency services, and a sensor that hears every shot can get officers moving where no one has called. An Illinois Criminal Justice Information Authority review found that adopting acoustic detection produced a sharp increase in dispatches to shots-fired incidents, which does suggest a real gap between gunfire that occurs and gunfire that is reported.

HOW THE COMPANY DESCRIBES IT

SoundThinking states an accuracy rate of 97% for identifying gunshots, based on the combination of its algorithm and analyst verification. It has credited the technology with substantial operational results in Chicago specifically, citing 125 lives saved over five years and the recovery of 2,985 firearms, figures it attributes to the police department.

Responding to independent criticism, the company said the MacArthur Justice Center's findings "relied heavily on a flawed analysis of incomplete data", and that the city inspector general's conclusions had been "misrepresented by critics to spread a false narrative" about accuracy. Its chief executive, on Chicago's cancellation, emphasised the technology's continuing positive impact for residents.

Both positions are recorded here because the accuracy dispute turns on a distinction the two sides do not share. The company's 97% figure is about whether a detected sound was gunfire. The critical research is about what happened after officers arrived. Those can both be true at once.

THE INDEPENDENT EVIDENCE

This is the most substantial adverse evidence base for any technology on this site, and it comes from two sources examining the same city.

The MacArthur Justice Center at Northwestern University School of Law analysed Chicago Police Department data covering roughly 21 months, from July 2019 to April 2021. It found that 89% of alerts turned up no gun-related crime, and 86% led to no report of any crime at all — approximately 40,000 deployments over that period that produced nothing.

Chicago's Office of Inspector General reached a compatible conclusion in August 2021, reporting that ShotSpotter alerts rarely produce evidence of a gun-related crime, rarely give rise to investigatory stops, and even less frequently lead to recovery of gun-crime evidence during such a stop. It also found the technology changes how officers interact with the communities where sensors are concentrated, and campaigners cite it as increasing stop-and-frisk activity.

WHAT HAPPENED IN CHICAGO

Chicago's contract history illustrates how these systems persist. A three-year, $33 million contract ended in 2021 and was quietly extended for two years at $9 million a year. Mayor Lightfoot's administration extended it again for $10 million while her successor was campaigning on ending it. The total value reached roughly $49 million.

Mayor Brandon Johnson announced cancellation in February 2024. The system continued through 22 September 2024 with a two-month transition, covering the Democratic National Convention. Houston, Atlanta and Cambridge, Massachusetts have also ended contracts with SoundThinking.

Campaigners point to a December 2018 incident in which two Chicago officers, Conrad Gary and Eduardo Marmolejo, were killed responding to a ShotSpotter alert near railway tracks — an argument about the risks created by rapid dispatch to an unverified location.

THE CASE FOR IT

The underreporting problem is real, and the Illinois review supports it. If a substantial share of gunfire generates no call, a technology that closes that gap has a genuine rationale, and the fastest possible response to a shooting can matter for a victim's survival.

The human verification layer is also a meaningful design choice. An analyst reviews flagged sounds before an alert is dispatched, which is a check most automated detection systems do not have.

THE CASE AGAINST

The strongest objection is not that the sensors mishear. It is that even accepting the company's accuracy claim, the operational result documented in Chicago was tens of thousands of deployments producing no evidence of any crime. A technology can correctly identify gunfire and still fail as a policing intervention.

The distributional consequence follows from where sensors are placed. Coverage is concentrated in particular neighbourhoods, so the additional police presence, the investigatory stops and the changed pattern of interaction all fall on those neighbourhoods, whether or not crime is found.

There is also a structural limitation no configuration fixes: a gunshot detection system cannot alert anyone until a shot has been fired. In an open street a fast post-incident alert retains value; as a preventive measure it does not exist.

Finally, the company now also owns the remains of Geolitica and HunchLab, giving one supplier both acoustic detection and place-based prediction — a consolidation worth watching given the evidence record of both product lines.

WHAT IS NOT ESTABLISHED

The 125 lives saved and 2,985 firearms figures are attributed to the police department by the vendor; no independent verification was identified.

The MacArthur analysis covers one city over 21 months. Whether the hit rate is comparable elsewhere has not been tested at similar rigour.

Whether cancellation changed gun crime outcomes in Chicago, Houston, Atlanta or Cambridge is not established by any source reviewed — a control the debate would benefit from.

How many agencies currently operate the system is not published.