When a man walked into San Francisco General Hospital last Thursday and fatally stabbed a social worker, he didn’t have to pass a security screening.
But even if he had entered the hospital’s most secure facilities, which house the bulk of its departments, he and his 5-inch kitchen knife might not have been stopped.
According to interviews with hospital staff and documents reviewed by The Standard, San Francisco General installed AI-enabled weapons detectors which have a track record of missing some weapons. Massachusetts-based Evolv Technology has been accused of overstating its ability to detect knives and guns — last year, it settled with (opens in new tab) the Federal Trade Commission over claims of false advertising, but did not admit wrongdoing.
In at least one instance, it allegedly failed to detect weapons at SF General. On Aug. 14, a man walked into the building with a loaded gun and a set of brass knuckles in a backpack undetected, according to a hospital worker familiar with the matter.
Security has proved to be a difficult balancing act, as the hospital has wrestled with whether a stronger police presence might deter vulnerable patients from seeking care.
SF General’s frontline staff say they’ve been voicing serious concerns about safety at the hospital campus for years — concerns they feel are not addressed with the installation of the new tech from Evolv.
“That company seems to have a lot of problems,” said Megan Green, a nurse on the hospital’s workplace safety committee. “How was it able to get that contract?”
‘Like Swiss cheese’
Traditional metal detectors generate magnetic fields. If you walk through a detector with a metal object, the field is disrupted, triggering an alarm. Metal belt buckles and keys set it off in the same way as handguns and knives.
Evolv’s sensors use similar magnetic fields, but they compare the signature of disruptions against a library of known weapons, according to patent documents. Evolv claims that, using machine learning, its detectors can distinguish between the magnetic signatures of guns and everyday objects such as phones and keys.
“In real life, it turned out to be a little more complicated than that,” said Nikita Ermolaev, a researcher at the security technology firm IPVM, which independently tests security products. The scanners cost upward of 20 times more than traditional metal detectors.
Evolv’s detectors have for years come under fire for allegedly failing to work as advertised.
In 2022, the BBC reported (opens in new tab) that Evolv produced but did not release a report that found its detectors couldn’t consistently flag knives and certain types of bombs. In 2023, a New York high schooler was stabbed to death (opens in new tab) with a 9-inch knife that allegedly passed undetected through Evolv scanners.
By 2024, New York City’s trial of the scanners in its subway system was dubbed “objectively a failure (opens in new tab)” by critics, and the FTC accused the company of false marketing.
Since then, Evolv has shuffled its executive ranks and improved its products, though Ermolaev said his firm has not been able to review how much more effective the detectors are.
In a statement, Alexandra Ozerkis, Evolv’s chief marketing officer, said the company “stands behind our technology.”
“Our technology has undergone rigorous third-party testing in recent years,” Ozerkis said. “That being said, nothing is perfect all the time. Evolv customers are keenly aware of the fact that safety is never absolute. Rather, it is a balance of safety needs with venue requirements.”
In a Nov. 20 disclosure (opens in new tab), the Department of Public Health acknowledged that it was planning to use Evolv systems as “part of the workplace safety program to assist in identifying and minimizing workplace safety risks.”
The disclosure highlighted the need for weapons detection specifically. “Based on the [Zuckerberg San Francisco General] annual security risk assessment, the lack of weapons detection is a contributing factor for patients entering the ZSFG hospital/clinics armed with sharp-edged weapons and replica firearms.” The hospital, along with all others in California, will be required by law to have weapons detection systems installed by March 2027 (opens in new tab).
In a statement, a spokesperson for the Department of Public Health said that the hospital was in the process of adding Evolv scanners in additional buildings, and would expedite installation because of the stabbing. “Scanners provide less intrusive screenings, minimizing patient anxieties who may be in crisis, as well as visitors,” the spokesperson said. “Since the weapons detections scanners were installed, thousands of weapons have been prevented from entering ZSFG, and the hospital continues to monitor the system’s effectiveness.”
Evolv’s documentation shows its detectors can be set to different sensitivity levels. At higher levels, fewer weapons will be missed, but the detectors will set off more false-positives — meaning they function like traditional metal detectors, Ermolaev said.
It is unclear what sensitivity level San Francisco General’s detectors are set to. But on Monday, The Standard observed that the hospital’s security screenings do not include bag checks or trays to deposit metal objects, which would be expected at high-sensitivity levels.
The guest who entered the intensive care unit with a gun and brass knuckles in a backpack was unaware of the contents, the anonymous hospital worker said, having brought the bag to return it to a patient. It’s unclear whether the visitor passed through the Evolv scanners, though the building’s entrances are guarded by them. A representative for DPH did not confirm or deny the incident.
“Even with the implementation of this system, our campus has so many holes. It’s like Swiss cheese in terms of security,” said Heather Bollinger, an emergency room nurse. “Health care is the most dangerous profession in the country. That is just wild.”
Ermolaev said Evolv leases clients its detectors on four-year contracts that can’t be canceled and cost as much as $120,000. Traditional metal detectors cost roughly $5,000.
“If a certain hospital in San Francisco does not want to install metal detectors because they look ugly, in their opinion, or they have this stigma of being a stupid device — that’s entirely up to them,” Ermolaev said. “As long as they know what they’re getting.”