Nashville’s police department has requested nearly $1 million for technology that alerts officers when a gun is fired. The goal is to get police to the scene of a shooting sooner.

But evidence of the tool’s effectiveness is mixed.

Often when someone fires a gun, no one calls 911. That’s where the company ShotSpotter comes in.

“If you’re living in a neighborhood and you’re awakened by gunfire, you look out your window, you expect to see a response. And if you don’t see it, you might attribute that to deliberate indifference,” says Ron Teachman, former chief of the South Bend, Ind., and New Bedford, Mass., police departments.

Teachman brought ShotSpotter to both cities before joining the company as a spokesperson in 2015. He says ShotSpotter is meant to alert officers to all the shootings that aren’t reported. Even if there’s no 911 call, officers and paramedics can come to gather evidence, talk to witnesses and render aid if someone has been hit.

“We try to change the narrative from the police aren’t there, well, now to the police are there, because they care,” he says.

The company makes big promises in its promotional videos. One advertisement says the technology “has been proven to identify and locate virtually all gunshots in less than 60 seconds.” ShotSpotter also tells law enforcement that it detects outdoor gunshots with a 97% accuracy rate. (The sensors do not pick up indoor gunshots.)

https://www.youtube.com/watch?v=FDoaTNVf85Y

Here’s how they say the system works:

Police departments pay ShotSpotter to install sensors in neighborhoods where they believe shootings are likely to happen. Then, when the sensors pick up a loud noise, ShotSpotter employees study the sound wave to see if it seems to be gunfire.

If they think there was a shooting, they alert police. Then, Teachman says, officers get pinged with information about the incident right on their cellphone or computer.

He says they receive a “host of intelligence about the event, such as how many rounds of fire, was there more than one shooter, high-capacity gun, full-automatic, a satellite view of the situation.”

A tool for ‘precision policing’

MNPD is asking for $800,000 for ShotSpotter, split over the next two fiscal years. ShotSpotter promotes itself as a tool for a philosophy called “precision policing.” Chief John Drake has made it one of three pillars of the Metro Nashville Police Department.

The idea is to focus law enforcement resources on the people and places officers believe are driving crime. Systems like ShotSpotter would theoretically make it easier for police to respond to more shootings more quickly.

Screenshot Courtesy Metro Nashville YouTube

John Drake speaks about precision policing at a Metro budget meeting in January 2022.

MNPD wouldn’t make anyone available for an interview about the technology. A spokesperson says if the funding request were approved, the department would study where to place the sensors, based on where officials expect most gunshot victims to be. But Drake emphasized his commitment to precision policing at a budget meeting in January.

“In a constantly growing city like ours, with more than 500 square miles, it is important that we are able to identify significant crime issues early on and quickly develop a precision police plan to prevent victimization,” he said.

Police, doctors and several researchers have praised ShotSpotter’s technology. Studies have found some areas that use it have seen declines in gun-related assaults, shorter response times and quicker transports to the hospital for gunshot victims. More than 100 cities have chosen to install the technology in their communities, according to ShotSpotter.

But multiple other researchers have cast doubt on the tool’s effectiveness.

‘What does the evidence tell us?’

Last summer, Chicago’s Office of the Inspector General published a report, which found that out of tens of thousands of ShotSpotter alerts that police responded to with a known outcome, officers discovered evidence of a gun-related crime only 10.9% of the time. Investigators also found that some officers used ShotSpotter alerts as a justification to conduct a stop or pat down when they might not have otherwise.

“The [Chicago Police Department] data examined by OIG does not support a conclusion that ShotSpotter is an effective tool in developing evidence of a gun-related crime,” the office wrote in a press release.

ShotSpotter said in a statement that the OIG’s findings did not necessarily mean that the alerts were false positives and that other factors, like trouble finding witnesses or a lack of physical evidence, could have affected officers’ arrest rates.

Another study published last year revealed counties that implemented ShotSpotter experienced no significant drop in gun violence, nor substantial increases in weapons-related arrests.

Courtesy Mitch Doucette

A graph in Doucette’s study shows large metro counties that implemented ShotSpotter followed similar trends for firearm homicide rates compared to those that did not. Implementers tended to have higher than average firearm homicide rates from the start.

“We always want to have the best interventions, right, the best ways to prevent violence and address violence,” says Mitch Doucette, an assistant scientist at Johns Hopkins’ Bloomberg School of Public Health who conducted the study on countywide violence data.

“Whenever there is a program or a technology or even a law that kind of proliferates across space and time, we want to understand, is the actions that are being taken, are those driven by evidence?” he says. “And, if so, what does the evidence tell us?”

Doucette’s team compared the number of homicides, murder arrests and weapons arrests in dozens of the country’s largest metro areas, to see if the ones with ShotSpotter had better outcomes. But he says installing ShotSpotter didn’t seem to have an effect — at least not on the county level.

Doucette said requiring a permit to carry a gun could be more effective at reducing violence. While his report found the counties he studied in states with gun permit laws experienced a 15% drop in firearm homicides, those in states with constitutional carry laws — like the one Tennessee enacted last year — had a 21% increase in killings with guns. The legislature is currently considering a bill that would allow even more Tennesseans to carry a gun without a permit, by dropping the age minimum from 21 to 18.

ShotSpotter calls Doucette’s study “problematic.” The company notes that it looked at crime trends on a county level – not in the specific locations where sensors were placed. ShotSpotter says the technology would have “little to no impact” on the trends outside its coverage area.

Doucette says his study isn’t perfect – that none is. But he still questions whether ShotSpotter is the best way to reduce gun violence and save lives. Beyond questions about the technology’s ability to impact violent crime, it is also expensive, he says.

“If that data does not lead to lower violence, does not lead to increased homicide clearance rate, nor does it lead to increased weapons arrests,” Doucette says, “then I would argue that perhaps those tax dollars could be spent in a better way.”