ShotSpotter gunfire detection system

ShotSpotter is an acoustic gunfire detection system manufactured by US-based company SoundThinking (named ShotSpotter until April 2023). Consisting of microphones, sensors, algorithms, and human reviewers, the system alerts police to potential gunfire.

ShotSpotter has been used by multiple municipal authorities, police departments and school districts across the US since 1997, and has been used as evidence in legal trials. 

According to Chicago mayor Lori Lightfoot, ShotSpotter 'plays an important role' in saving lives. However, the system has also proved controversial, with concerns noted about its effectiveness, fairness, reliability, privacy, transparency, and accountability.

Risks and harms

Accuracy/reliability

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

• 63-year-old Michael Williams was wrongly arrested and jailed for a gun murder on the basis of an 'unreliable' ShotSpotter gunshot detection alert.

• 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'.

• 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.'

• 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.

Oversight/review

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 percent 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 suggested SoundThinking analysts 'frequently modify alerts at the request of police departments' - a conclusion also reached by the AP. VICE and AP's accounts were strongly contested by SoundThinking.

Bias/discrimination

ShotSpotter has 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.' 

Privacy

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.

Transparency

• 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.

Investigations, assessments, audits

• Edgeworth Economics (2023). Independent Audit of the ShotSpotter Accuracy, 2019-2022 (pdf)

• CAG Analysis (2011). ShotSpotter Efficacy Study (pdf)