Critics say the numbers — just 19 percent of the gunfire alerts in the last 25 months even led to an offense report — do not justify the $3.5 million cost of the controversial tool. In the remaining cases, officers were dispatched based on the alerts but did not find any evidence, such as shell casings.
Authorities filed 126 charges related to ShotSpotter alerts, including one capital murder charge, according to Houston Police Department Assistant Chief Milton Martin, who presented an update to a City Council committee last week. Half of those charges involved misdemeanor offenses, most commonly the illegal discharge of a firearm in the city.
Not directly reflected in those statistics, Martin said, is the intelligence that HPD was able to gather from ShotSpotter data. Because residents do not always call 911 to report every gunshot they hear, the tool has allowed officers to map out areas where gunfire problems are the most severe and deploy its resources accordingly, he said.
"Just in the first year of operation, over 200 shell casings that we collected were linked to firearms that were used in other crimes in other parts of the city," Martin said. "While that's not an automatic 'Oh, now we know who to arrest,' it's information that investigators did not have before."
Some advocates, however, say the numbers do not justify the cost of the program: $3.5 million for a five-year contract from 2022 to 2027 at an annual price of approximately $74,000 per square mile.
"Only 20 percent of alerts result in an offense support, meaning that 80 percent of responses are a waste of public resources," Christopher Rivera, outreach coordinator at the Texas Civil Rights Project, said. "I believe that we can use the $3.5 million...and put it into programs that actually reduce gun violence, like housing and health care and debt relief."
The ShotSpotter gunshot detection system uses sensors placed in communities to pinpoint the location of suspected gunfire. Every time the system detects a potential gunshot, it sends a short clip of the recording to ShotSpotter technicians, who listen to the clip, verify that the sound is gunfire and send the information to partner law enforcement agencies.
The statistics that Martin presented only pertain to the first ShotSpotter zone, covering five square miles on the southeast side, that was set up in December 2020. No data was available on the second zone, a five-square-mile area on the north side, that has been operational for the past six months. Martin said that is because HPD has not yet integrated ShotSpotter with its other computer systems and officers have not had time to manually go through all the data from the newer zone to produce a report.
Because ShotSpotter offers more precise location information than most 911 callers, police have treated the alerts with more urgency than they do regular reports, Martin said. While officers do not always immediately respond to a call about gunfire, the department dispatches an officer to investigate almost every alert.
"We treat (a ShotSpotter alert) as a very high priority call and we run over there as quickly as we can," he said. "And that, I think, has resulted in a lot of those arrests that we made. People didn't expect us to get there as quickly as we did."
Meanwhile, critics and studies of the system in other cities raise questions about the accuracy and efficacy of the gunfire detection tool.
Little consensus exists even among officials who have adopted the technology. In Texas, San Antonio canceled its contract in 2017, after just one year of operation, saying that ShotSpotter simply was not worth the money. Harris County officials, however, have called ShotSpotter a "godsend" for the Aldine area.
Chicago's former Inspector General Joe Ferguson said Houston's statistics so far are "in the same universe" as those in other parts of the country that have been subjected to criticism by experts.
The author of a 2021 report by Chicago's Office of Inspector General, Ferguson found that ShotSpotter alerts rarely led to evidence of a gun-related crime and could result in biased policing behaviors. He cautioned Houston officials against making premature conclusions based on ShotSpotter data during an interview with the Chronicle.
"What was found in Chicago and has been found in other places is the false positive rate is over 50 percent," Ferguson said. "And people don't understand that. People assume things are worse than they are. That spawns fear, and fear spawns overreaction, both as a political matter and in terms of response in the field and on the street."
At the same time, Ferguson applauded Houston's incremental approach to implementing the program.
"The way that Houston is going about it is the way that these things should be approached. It started with a pilot program, it is focused, it generates the data, and the data is subjected to analysis and made publicly available," he said. "But the results that they've gotten so far aren't significantly better than what has been reported nationally."
Despite skepticism from some experts and advocates, some Houston officials are eager to take advantage of the law enforcement tool. Outside the two existing zones, a number of council members are considering purchasing additional ShotSpotter services to install detectors in neighborhoods that are demanding the technology.
District A Councilmember Amy Peck already has allocated a portion of her Council District Service Fund to buy one square mile of ShotSpotter utilization. District J Councilmember Edward Pollard is speaking with several management districts about sharing the cost of a potential purchase.
"I'm hopeful that it will be very beneficial so that we can combat some of these gunshots that we're hearing constantly in my district," Peck said. "But it is very expensive, and we are going to be looking at the data to make sure that it's something that we want to continue."
District C Councilmember Abbie Kamin, who chairs council's Public Safety and Homeland Security Committee, called the number of alerts "startling." She said she wants to enable all districts who wish to participate to be a part of the ShotSpotter program.
"I think the fact of the matter is we have a gun violence epidemic, and it's far larger in scale than many people realize and even HPD realizes," Kamin said. "Without this technology, we wouldn't even know the scale to which we're dealing with it."
Ferguson, on the other hand, said that judging from other cities' experience, a ShotSpotter utilization model based on neighborhood interests or complaints has seldom resulted in sound decisions.
"What happens is we're implementing a technology on the basis of under-informed and politically tinged decisions by people who actually themselves don't understand the value of this thing," Ferguson said. "It may make the councilman feel like he's responded to constituents. It may make the constituents feel better. But that's not a rigorous way of going about this."
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