ShotSpotter gunshot detection system

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ShotSpotter (renamed SoundThinking in April 2023) is a US-based company that manufactures an acoustic gunshot detection system (still named ShotSpotter) consisting of microphones, sensors, algorithms, and human reviewers that alerts police to potential gunfire.

The ShotSpotter system is used by municipal authorities, police departments and school districts across the US, and has been used as evidence in legal trials. Per the BBC, there are clear examples of the system working. According to Chicago mayor Lori Lightfoot, ShotSpotter 'plays an important role' in saving lives.

However, ShotSpotter has also proved controversial.

Accuracy, reliability

SoundThinking claims 97% accuracy and 0.5% false positive rates across its ShotSpotter customers. But a number of third-party studies appear to undermine this claim, raising questions about the system's effectiveness and value. 

A May 2021 study by researchers at the MacArthur Justice Center at Northwestern University’s School of Law found ShotSpotter sent Chicago Police Department (CPD) officers on over 40,000 'dead-end deployments'  and concluded the tool is 'too unreliable for routine use'. The CPD had signed a three-year, USD 33 million contract with ShotSpotter in 2018. 

A 2021 report by Chicago's Investigator General into the use of the system by Chicago police (CPD) concluded 'CPD responses to ShotSpotter alerts rarely produce evidence of a gun-related crime, rarely give rise to investigatory stops, and even less frequently lead to the recovery of gun crime-related evidence during an investigatory stop.'

The report also questioned the 'operational value' of the system and found that it increased the incidence of stop and frisk tactics by police officers in some neighbourhoods.

A 2022 AP investigation reported ShotSpotter has 'serious flaws' in its technology that called into question its effectiveness and value, and undermined the company's marketing claims. The investigation found ShotSpotter's system was unreliable, can miss live gunfire directly under its microphones, and may misclassify car backfires and firework sounds as gunshots.


Questions have been asked about the degree to which human analysts assess and modify ShotSpotter alerts.

SoundThinking/ShotSpotter revealed to AP that alerts are modified 10% of the time, and that it stopped showing the system's algorithm’s confidence rating to human reviewers in June 2022 'to prioritize other elements that are more highly correlated to accurate human-trained assessment.'

A July 2021 VICE News report, citing the May 2020 arrest, charging and jailing of 63 year-old Michael Williams for a gun murder that was later overturned on the basis of insufficient evidence, suggested SoundThinking analysts 'frequently modify alerts at the request of police departments' - a conclusion also reached by the AP.

At Williams' trial, prosecutors cited ShotSpotter sensors to bolster their case. But, according to a motion (pdf) filed by Williams' , the company’s algorithms had initially classified the sound as a firework and that the location co-ordinates had been altered, persuading the prosecutors to withdraw ShotSpotter evidence against Williams. 

The VICE and AP accounts were strongly contested by SoundThinking.


SoundThinking/ShotSpotter has also been accused of discrimination against minority communities. VICE News reported the system was used 'almost exclusively' in non-white communities in Atlanta, Chicago, Cleveland, and Kansas City. 

According to attorneys for Chicago-based community groups, ShotSpotter's lack of accuracy and its use in predominantly Black and Brown communities feeds 'racialized patterns of overpolicing.' 


Civil liberty and privacy advocates have expressed concerns about the use of ShotSpotter microphones and sensors in public spaces and their proximity to housing, and worry that it may set a poor precendent. 

Concerns have also been expressed about the length of time aural data is retained by SoundThinking, and how secure it is.


Claims that the ShotSpotter system has 'serious flaws' that appear to contradict what SoundThinking says publicly has led to accusations that its marketing is misleading and hyped.

SoundThinking has also been criticised for refusing to provide access to the ShotSpotter system so that its claims of accuracy and reliability can be independently peer-reviewed or assessed.

Given ShotSpotter's use in court, the company's lack of transparency 'isn’t acceptable', according to the ACLU.

Operator: Chicago Police Department; Houston Police Department; New York Police Department
Developer: SoundThinking/ShotSpotter
Country: USA
Sector: Govt - police
Purpose: Detect gunfire
Technology: Gunshot detection system
Issue: Accuracy/reliability; Bias/discrimination - race, ethnicity, income, location; Effectiveness/value; Oversight/review
Transparency: Governance; Black box; Marketing; Legal


Legal, regulatory

Research, advocacy

Investigations, assessments, audits

News, commentary, analysis

Page info
Type: System
Published: May 2022
Last updated: May 2023