Gun owners ought to keep a close eye on how authorities pair gunfire-detection microphones with license-plate cameras in public safety systems.
Flock Safety, the leading supplier behind the recently debated roadside camera network that reads passing plates, offers more than just automated license plate readers (ALPRs). The company also markets a broader surveillance package dubbed the “Safe City” subscription. Promoted as Flock’s “Most Complete Solution”, the “Safe City” package combines the frequently discussed ALPRs with a live video feed—and a gunfire microphone. Putting these instruments together raises the possibility that law-abiding gun owners could become suspects merely because they happen to be nearby.
Reliable data on how many active gunfire microphones exist in the United States is scarce. The Electronic Frontier Foundation’s Atlas of Surveillance catalogs close to 250 gunshot-detection deployments and purchase plans nationwide, though many of these programs have since ended. Municipalities have also rolled out firearm-detection systems that use AI to identify visible firearms on video or to blend acoustic sensors with dual-sensor infrared cameras to spot gunshots.
Flock stands among a broad array of suppliers in the global gunshot-detection market, a sector valued at roughly $1.5 billion in total. Yet the company’s marketing materials raise concerns about what the technology can actually do beyond simply detecting gunfire. In Flock’s own words, a verified gunshot can surface the vehicles seen entering or leaving the vicinity around the moment the sound occurred, using nearby Flock license-plate-reader cameras. That claim warrants careful scrutiny, because it describes a process that could translate a suspected gunfire event into a list of nearby vehicles.
Innocent gun owners could end up appearing on such lists. If a bang picked up by a microphone is mistaken for gunfire (which could happen with a similar noise that triggers a false positive), that identified event can prompt an ALPR query that sweeps up drivers with no connection to the incident. With more than 20 million carry permits in circulation and 29 states not mandating them, a sizeable share of those motorists are legally armed. The mere proximity of those drivers might be misread as proof they fired the shot.
This prospect triggers two legal questions for lawful gun owners. First, what justification exists for stopping someone who appears on such lists? Second, does querying the ALPR database amount to a search under the Fourth Amendment? Recent court decisions have begun to offer some guidance.
In the Supreme Court’s 2022 ruling New York State Rifle & Pistol Association v. Bruen, the right to lawful public carry was affirmed. In the 2024 case United States v. Daniels, the Tenth Circuit Court of Appeals remarked that no crime had been reported when an unarmed man was detained after a 911 caller’s description did not match him. Citing Bruen, the court stated it cannot view citizens—as long as they are lawfully exercising their Second Amendment rights—with suspicion.
Last May, in Commonwealth v. Foster, the Pennsylvania Supreme Court reached the opposite conclusion: police can stop someone in response to late-night gunfire alerts from a microphone, even when only two individuals are present and when the observed behavior seems evasive. An investigative stop requires probable cause or reasonable suspicion tied to concrete facts linking a person to suspected criminal activity. The worry is that an alert, combined with a plate-match, might be treated as enough for reasonable suspicion, even if only proximity is established.
A more recent New Jersey decision underscores that risk. In State v. Carrillo, a state appellate court ordered suppression of evidence (an unlawfully held handgun) found during a minivan stop followed by a warrant-backed search. The court ruled that the gunshot alert and an ALPR hit did not sufficiently tie the minivan to the earlier shooting. Prosecutors admitted that video thought to show muzzle flashes from the minivan at the time of the shooting actually depicted nothing of the sort.
When police seek evidence inside a vehicle, that qualifies as a search. But does querying an ALPR database count in the same category?
In United States v. Porter, the Fifth Circuit in March held that using a ten-camera ALPR network to locate a known vehicle did not constitute a search. A few months later, in Chatrie v. United States, the Supreme Court ruled that obtaining Google location records to identify people near a crime scene amounted to a search. Roadside camera observations differ from exact phone-location data, but an alert-driven ALPR query bears closer resemblance to the situation in Chatrie.
Proponents of gunshot microphones argue that gunfire on city streets is typically illegal and that rapid responses save lives and lower violence. Yet a federally funded evaluation of the gunshot detector ShotSpotter in Chicago and Kansas City found that, although responses were expedited and more guns were recovered, there was no corresponding drop in shootings or improvements in clearance rates.
With state legislatures slow to act, municipalities must chart their own course between safety and privacy. Absent a full ban on every aspect of the Flock bundle, city councils should codify four safeguards to protect residents’ rights.
First, police should generally obtain a warrant—setting time and distance bounds—in the case of an alert-initiated ALPR query, except in true emergencies. Second, cities should not connect gun-detection alerts to ALPR data without a public hearing and a formal vote. Third, every query must be logged for oversight, and information about vehicles not involved in the case should be purged once it ceases to be required as evidence. Fourth, a stop or search based solely on an alert plus proximity should not be permissible.
Every city that uses gunshot-detection technology is facing a renewal or replacement decision. Those deliberations should publicly disclose the rules governing the interaction between gun-detection systems and ALPRs. Because these tools can be bundled, the limits on surveillance matter no matter which vendor a city considers. Whether expanding an existing network or evaluating a replacement, the privacy safeguards should be fixed before signing the next contract.
