ShotSpotter: A Primer

By Doug Breehl-Pitorak

Updated Oct. 12, 2022

On Oct. 10, Cleveland City Council passed legislation that would use about $2.75 million of American Rescue Plan Act (ARPA) funds to expand ShotSpotter, a gunshot-detection technology, to cover 13 square miles of the city. After several weeks of debate, council added into the legislation an additional $150,000 for an independent evaluation of the technology.

Here’s what we’ve learned about how ShotSpotter works, how much it costs, and what questions using it raises:


How does ShotSpotter work?

This gunshot-detection technology uses a combination of acoustic sensors and computer software to detect gunshots and alert customers -- generally police forces -- about incidents. Here’s how the company says it works:



ShotSpotter says that the process -- from gunshot to alert or dismissal -- takes 60 seconds or less.

What is the price tag?

Cleveland’s pilot program in the Fourth Police District cost $449,000, Cleveland Police spokeswoman Sgt. Jennifer Ciaccia said in an email. A grant from the Cleveland Police Foundation covered $375,000 of that cost. The city covered the remaining $74,000.

The city’s proposed $2.75 million expansion using ARPA money is for three years.  An annual subscription in the current contract costs $65,000 per square mile.

Does ShotSpotter accurately detect gunfire?

During a five-month span in 2021, ShotSpotter’s staff reviewed 16,102 detections in the pilot area, according to records Cleveland Documenters obtained from the city. They dismissed about 88 percent of ShotSpotter detections as non-gunfire sounds. Roughly 12 percent were sent to police as a gunfire or probable gunfire alert.

Of the 1,910 incident alerts sent, CDP reported issues with less than one percent of them, including two gunfire incidents that ShotSpotter said weren’t gunfire and one that ShotSpotter didn’t detect and report to police.

ShotSpotter relies on customers to report inaccuracies.


To respond to questions about accuracy, ShotSpotter commissioned Edgeworth Analytics, a data science company, which confirmed the company’s claim of 97 percent accuracy at differentiating gunfire from other sounds.

Is it effective?

Depends on who you ask.

Cleveland police credit ShotSpotter for helping save four lives because the ShotSpotter alert “was received well before any calls from the public, and our response was half that of a typical Priority One response,” according to a six-month report reviewing the program’s impact from November 2020 through April 2021.

With about 15 percent of gunfire incidents being called in by the public, the report says ShotSpotter had generated more than 1,000 runs in the pilot area that police otherwise wouldn’t have made.

Alerts, the report says, also resulted in:

  • 217 incidents with bullet casings recovered
  • 142 investigative leads
  • 24 recovered guns
  • 25 arrests

For all of 2021, ShotSpotter led to 34 gun recoveries, 28 arrests, and six saved lives, according to Cleveland.com.


In Canton, however, city officials ditched ShotSpotter in 2019 after six years for a different, cheaper service, according to the Akron Beacon Journal. Former Canton Police Chief Jack Angelo said moving ShotSpotter sensors was difficult and costly, and he noted there weren’t a lot of arrests after the technology was installed. Canton officials said 100 percent of gun-detection alerts were accompanied by community calls, compared to 15 percent in Cleveland. And the technology detected one gunshot per day on average in Canton, according to reporting by Cleveland 19 News.

In terms of preventing gun violence, the effect of ShotSpotter isn't clear. An analysis of data from 68 large metropolitan counties in the United States from 1999 to 2016 found that ShotSpotter had no significant impact on firearm-related homicides or arrest outcomes.

What concerns have been raised about ShotSpotter?

ShotSpotter is used in more than 100 cities. As it has expanded, so have concerns about its effectiveness compared to its cost and the overpolicing and surveillance of Black and brown communities.

Effectiveness at solving and preventing crimes

A 2021 report from Chicago’s Office of Inspector General concluded that Chicago Police responses to ShotSpotter alerts “rarely produce documented evidence of a gun-related crime, investigatory stop, or recovery of a firearm.”

The report acknowledges a study on ShotSpotter's impact in St. Louis that found an 80 percent overall increase in the volume of police responses to reported gunshots – but no significant reduction in crime attributable to the ShotSpotter sensors.

Affecting officers’ perception of -- and behavior in -- areas with high ShotSpotter alerts

The inspector’s office also found that “the introduction of ShotSpotter technology in Chicago

has changed the way some CPD members perceive and interact with individuals present in areas

where ShotSpotter alerts are frequent.” Specifically, some officers used their knowledge of where ShotSpotter alerts occur as “additional rationale to initiate a stop or to conduct a pat down once a stop has been initiated.”

In Cleveland, ShotSpotter alerts have led to “potentially unconstitutional stops and searches,” according to reporting by Matthew Richmond for Ideastream.

Shaky use as evidence

In a Sept. 19 public comment urging City Council to vote no on the proposed expansion, Matthew Ahn, a Ward 3 resident and Cleveland State University law professor, referenced numerous concerns with the technology, including claims that ShotSpotter works with police to alter reports and whether it is considered unreliable evidence by prosecutors. An officer in Rochester, N.Y.,  shot Silvon Simmons three times in the back in 2016, alleging that Simmons fired first. ShotSpotter initially classified sounds from that incident as helicopter sounds but adjusted its report three times after learning the police were investigating a shooting.

A jury found Simmons not guilty of attempted aggravated murder and attempted aggravated assault of a police officer. A judge later reversed an initial conviction on a gun possession charge, saying it was based on flawed ShotSpotter evidence.  

Chicagoan Michael Williams spent nearly a year in jail before a judge dismissed a case alleging he murdered Safarian Herring in 2020. Prosecutors had used ShotSpotter evidence to build the case but ultimately said the evidence was insufficient.

ShotSpotter says its evidence and witness testimony has been accepted in more than 200 court cases across 20 states.

Privacy concerns

Concerns about privacy and surveillance have been raised, too. Cleveland’s Community Police Commission (CPC), an oversight body established by the city’s Consent Decree with the U.S. Department of Justice, shared a report in May from its Search and Seizure Work Group, Technology Committee. CPC formed the committee to examine best practices for implementing crime-prevention technology without infringing upon civil liberties.

“At this stage in our inquiry we have found no evidence that these technologies were implemented in the spirit of the Consent Decree, where the entire community was engaged in evaluating the proposal from the onset and their values were represented,” the report says about ShotSpotter and  technologies such as cameras and license-plate readers.

The American Civil Liberties Union (ACLU) has raised concerns generally about microphones being placed in public spaces, though it said it doesn’t think ShotSpotter posed an active threat to privacy.

A report from the New York University School of Law Policing Project determined “the risk of voice surveillance was extremely low.”

What do you think?

Want to make a public comment about ShotSpotter? You can try to register for public comment at City Council’s 7 p.m. Monday meetings. Here is a guide to registering.

Do you have questions we haven’t answered? Submit them here. If you have experience with ShotSpotter, we’d like to hear about it. Email us at cledocumenters@gmail.com.

[Check out Cleveland Documenters coverage of the ShotSpotter debate during two recent City Council meetings:


Correction: A previous version of this primer said the expansion in Cleveland would cover an additional 13 square miles. The expansion will result in 13 covered square miles total.