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School Climate & Safety

Schools Turn to AI to Detect Weapons. But Some Question the Tech’s Effectiveness

By Evie Blad — April 12, 2023 9 min read
A computer screen shows a man walking between two vertical sensors at the entrance to a building. An orange cube shape illuminates over his hip, suggesting a weapon has been detected under his clothing.
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It took less than a year for leaders in the Utica City School District in New York to regret spending $3.7 million on artificial intelligence systems designed to keep weapons out of schools. They quickly reversed course when the technology failed at the one thing they expected it to do.

Last October, a high school student stabbed and injured his classmate, using a knife that the scanners apparently failed to detect.

What followed was a debate about the machines’ effectiveness, complaints about the limits of the technology, and a decision to phase them out.

The AI systems, made by a company called Evolv Technology, remain in the district’s elementary and middle schools. But officials have replaced them with “airport style” metal detectors and bag scanners at the high school. It takes students longer to pass through, but administrators also have more confidence they will detect weapons like knives and cans of pepper spray, acting Superintendent Brian Nolan said.

“It may stop someone with a bomb or a rifle, anything like that,” Nolan said of the Evolv system. “But the practical application for a high school, the primary weapon of choice for a high school student is a knife. They didn’t catch that.”

The Utica machines also missed a gun, Nolan said. A staff member at another school told him that a police officer, who was also a parent, passed through one of the scanners with his service weapon, which went undetected.

As districts around the country respond to concerns about community violence, student behavior, and school shootings, a growing number have turned to AI systems to keep weapons out of their buildings.

Makers of the systems, which use a combination of AI software, cameras, and electromagnetic sensors to detect possible weapons as students walk past, sell their products as a highly effective alternative to the traditional metal detector that allows users to avoid long lines. The systems are also used by major sporting venues to screen fans attending professional sporting events.

But their adoption has not been without frustration. Some districts, like the Urbana, Ill., school system, have reported consistent false alarms with common items like water bottles and Chromebooks, creating new challenges at building entrances. Officials in the Charlotte-Mecklenberg, N.C., schools recorded videos showing students how to hold frequently misidentified objects in their outstretched arms so staff monitoring the scanners can easily see what triggered the sensor.

Reducing the machine’s sensitivity will reduce false alarms, but it may also reduce the technology’s effectiveness at detecting legitimate weapons, like guns, administrators told Education Week.

Administrators who support the use of AI scanners say that, while they may not be a definitive solution to concerns about school violence, they have helped reduce weapons reports and served as a deterrent. Part of the job, they say, is adapting to the quirks of the technology so that it can be more effective.

“Technology has limitations, and we have to understand that and work around those limitations,” said Ronald Applin, director of safety and security for Atlanta Public Schools, which installed Evolv detectors this year.

Growing use of AI weapons detection in schools

A growing number of school districts, including eight of the 100 largest in the country, have installed AI weapons detection systems in the past two years. Local news reports suggest some school systems have used federal COVID-19 relief funding to cover the expense. The machines rely on ongoing software fees to operate, which means the districts will shoulder continuing operations costs when that time-limited federal aid expires.

Evolv, one of the largest providers of AI security technology for schools, said recently that the K-12 sector represented half of its business in the fourth quarter of 2022—alongside clients like Atlanta’s Mercedes-Benz Stadium, where the city’s NFL team, the Falcons, play.

K-12 “continues to be our No. 1 end market,” Evolv CEO Peter Gustav George said in a March 2 earnings call. “We partner with our customers to create safer zones in over 400 school buildings, up from 200 at the end of the third quarter.”

Technology has limitations, and we have to understand that and work around those limitations.

School security vendors often see a surge of interest after school shootings, like the May 2022 attack at Robb Elementary School in Uvalde, Texas. Conversations about “hardening schools” with physical security measures, including AI and other weapons detections systems, started anew after six people died in a March 27 shooting at a private elementary school in Nashville, Tenn.

About 2.7 percent of all public schools and 7.7 percent of high schools reported daily student checks with traditional metal detectors in the 2019-20 school year, according to the most recent federal data. Six percent of all schools and 14.8 percent of high schools reported random sweeps with metal detectors.

While metal detectors and AI scanners may help keep some weapons out of schools, they are less likely to prevent a mass shooting, Ohio-based school safety consultant Kenneth Trump said. Attackers intent on committing mass violence are known to shoot through secure doors, as the Nashville shooter did, or openly carry weapons into buildings. (In Denver, a high student shot and wounded two staff members on March 22 as they conducted a routine weapons search.)

An increase in school weapons reports

While mass shootings drive school safety conversations, some school districts that use systems like Evolv’s point to day-to-day concerns about weapons in their buildings as a motivation for installing them.

Atlanta schools installed Evolv scanners this year in some building entrances, particularly those where large numbers of bus riders pass through at once, to supplement the use of traditional metal detectors at other entry points, Applin said. By this time last school year, the district had confiscated 30 guns from students, he said. This year, they’ve confiscated seven so far.

It’s not a foolproof system. Some students managed to bypass scanners by passing the guns through windows or side doors their peers opened for them, Applin said.

Charlotte-Mecklenburg schools installed Evolv scanners at its high schools after finding a record 31 firearms on students during the 2021-22 school year, Chief Operations Officer Brian Schultz said.

“Coming out of COVID, we saw increased physical aggression, increased firearms,” he said. “This is a problem around the country.”

The district’s use of Evolv scanners was the subject of an August 2022 investigation by Vice News, which relied on 2,000 internal emails to reveal problems with its rollout. Officials at another school district had warned Charlotte-Mecklenburg administrators that it had been able to pass a Glock handgun through the scanners without detection, Vice reported.

Administrators also complained of long lines at the scanners, error messages, and false alarms that detected “weapons of mass instruction,” like Chromebooks.

The process has improved in the time since, Schultz told Education Week. Administrators made videos to show students how to pass through the machines and to hand off frequently flagged items like umbrellas to supervising staff beforehand.

The district has found four firearms on students this school year, Schultz said, although some were located by word-of-mouth after students brought them into school through another entry point.

“Our students have become a lot more vigilant about reporting those kinds of things,” Schultz said. “Relationships trump any system you have.”

‘No perfect solution’

Independent school safety consultants warn about the effectiveness of the scanners and have called for more data about their effectiveness.

In November 2022, BBC News reported that a private evaluation of Evolv machines showed that, in 24 trial walkthroughs, they failed to detect knives 42 percent of the time. That detail was among those omitted from a shorter version of the evaluation that Evolv released publicly, leading some attorneys to claim the company had participated in deceptive marketing tactics.

At EdWeek’s request, Evolv initially scheduled an interview with one of its executives to respond to questions about the technology. But it later cancelled the call, citing a busy travel schedule, and a spokesperson responded to questions by email instead.

“There is no perfect solution that will create a completely sterile environment and catch all weapons for schools or any venue,” Anil Chitkara, Evolv’s co-founder and chief growth officer said in an emailed statement. “This is why a layered approach of people, process, and technology is used in security planning and execution—and schools are no different.”

Evolv acknowledged that its machines flag some everyday items that have the “composition and profile of component parts” of weapons. But, as the AI technology continues to “learn” to better distinguish everyday objects from weapons, the company offers software updates to its customers, Chitkara said. In the fourth quarter of 2022, Evolv machines around the country “tagged nearly 70,000 weapons—including 36,000 guns and 33,000 knives,” he wrote in the email.

The company also denied misleading marketing. Evolv doesn’t want to provide a “blueprint” of vulnerabilities to bad actors by revealing too much, Chitkara said in the email response.

While “public-facing marketing materials are intentionally not specific,” he said the company communicates all “limitations and capabilities” of the system with potential customers.

Most district administrators who spoke with EdWeek would not discuss the settings they used on their Evolv systems or possible error rates, citing security concerns.

In Atlanta, Applin acknowledged that no machine is perfect. The district, like Charlotte-Mecklenburg, also relies on student tiplines, security cameras, and student awareness campaigns to prevent violence and determine if there are weapons on campus.

“If someone wants to get something into the building, they are going to find a way to do it,” Applin said.

Evolv's Response to EdWeek's Questions

Evolv responded via email to Education Week’s questions on the technology. Here is the full response from Anil Chitkara, the company's co-founder and chief growth officer.


Why are more schools considering weapons detection technology?


According to Education Week’s school shooting tracker, 2022 ended with 51 school shootings that resulted in injuries or death and at least 300 shooting incidents on school grounds. Beyond those troubling statistics, we have heard from schools that they are experiencing an increase in the number of firearms being brought to school.


Knowing that to mitigate risks, every second counts, as does the technology, people, and processes in a layered security approach, one solution school districts are considering is weapons screening.


On the increase in school districts using Evolv to detect weapons


We are now in more than 400 school buildings across the country, including Manassas School District, Wyoming Valley School District, Niagara Falls School District and Winnebago School District.


Are there any differences between Evolv's applications in schools vs. other environments, like sports arenas?


The Evolv Express system being used in schools is the same technology that is used by customers in other industries, like sports stadiums and theme parks.


Each location is unique in their security needs, even from one school to another. We work with each customer to determine how best to integrate our technology into their overall security plan.


Some schools are concerned that Evolv systems detect items like Chromebooks when the sensitivity is turned up high enough to detect guns.


There are some everyday items that have the composition and profile of component parts of threats we seek out; some Chromebooks fall into that category. Each school that considers our technology understands this and determines whether the system is the right addition to their security plan.


It’s important to understand that our advanced threat detection continues to learn and become better at distinguishing weapons through AI technology. Evolv then provides those improvements via a software release available to all subscribers. Our customers determine when they upgrade the software.


Some schools have expressed concerns about systems not detecting knives.


Our customers used Evolv Express to tag over 176,000 weapons in 2022—including 93,000 guns and 83,000 knives. In the fourth quarter alone, they tagged nearly 70,000 weapons—including 36,000 guns and 33,000 knives. That’s an average of about 400 guns every single day.


There is no perfect solution that will create a completely sterile environment and catch all weapons for schools or any venue. This is why a layered approach of people, process, and technology is used in security planning and execution—and schools are no different.


Evolv’s response to the BBC investigation into the systems and subsequent announcements by law firms about possible lawsuits.


Evolv Express systems are designed to detect various types of weapons, and components of weapons, that could cause mass harm, not items that are readily available within schools. There is no perfect solution that will stop 100% of threats, including ours, which is why security must include a layered approach that involves people, process, and technology. 


The best technology is transparent as to what it does without disclosing a “blueprint” to a bad actor that could use it to do harm. Those in charge of keeping buildings safe must assume that bad actors are always looking for ways to circumvent the security processes in place. It is devastating that this concept even applies to schools, but it must. 


This is a best practice well known in the security industry, notably the TSA. The TSA carefully guards Sensitive Security Information (SSI) to keep the public safe. SSI is information that, if publicly released, would be detrimental to transportation security, as defined by Federal Regulation 49 C.F.R. Part 1520.


Marketing weapons detection security requires a delicate balance between educating stakeholders on new technology and not providing bad actors with the information they could use to do harm. So, while public-facing marketing materials are intentionally not specific, we communicate all aspects of the Evolv Express system—including limitations and capabilities—with the trusted security professionals at our customers, partners, and prospects.


If you have any questions about specific lawsuits, we can direct you to our legal team.

“We sometimes have the impression that this is going to solve all of our problems, but it doesn’t work that way,” he continued. “But when I look at the results from last year to this year … we know that the numbers [of gun reports] have been reduced significantly.”

After the stabbing incident in Utica, administrators determined a previous superintendent had erred when he told the school board the Evolv system would detect all weapons, including knives, said Nolan, the acting superintendent.

The machines still in place in the district’s elementary and middle schools are now turned up to the highest sensitivity level in hopes they will be more effective at finding harmful objects. But that means they also alarm on some benign items, too, Nolan said. This year, a mother called him to say her young daughter was in tears after her metal lunch box triggered an alarm and a subsequent search.

AI systems may be a good solution for schools in the future, after years of development and refinement, Nolan said. But for now, he’s determined they are not the right solution for Utica.

“It’s a tough situation when you think about the money you are spending, that it doesn’t give you the assurance of safety,” Nolan said. “People who are considering it should understand what it will and won’t do for you.”

A version of this article appeared in the April 26, 2023 edition of Education Week as Schools Turn to AI To Detect Weapons

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