For years, the privacy debate around automatic license plate readers focused on a specific question: is it acceptable for cameras to record where your car has been? Companies like Flock Safety, which operates cameras in over 6,000 communities, argued that they track vehicles, not people. The distinction mattered legally and politically — tracking a car felt less invasive than tracking a person.
That distinction just evaporated.
A defense contractor called Leonardo is marketing a product called SignalTrace that adds wireless sensors to existing license plate cameras. These sensors do not photograph anything. Instead, they capture the electronic signals broadcast by every device in and around a passing vehicle. Your smartphone, your wireless earbuds, your smartwatch, your fitness tracker and your car's infotainment system all emit signals that SignalTrace can detect, catalog, and associate with your license plate. Leonardo's own materials go further, listing key fobs, work access badges, tire pressure sensors and pet microchips — claims that, as we set out below, an independent researcher has since called into question.
The result is what Leonardo calls an "electronic fingerprint" — a unique combination of device identifiers that travels with you everywhere you go. License plate cameras no longer just know where your car has been. They know who was inside it.
Most people do not realize how many wireless signals their vehicle emits at any given moment. SignalTrace is designed to capture all of them.
Your phone constantly broadcasts Bluetooth and Wi-Fi probe requests, each containing unique identifiers. Even when not connected to anything, most phones scan for available networks and devices, announcing their presence to any receiver within range. This is how SignalTrace detects your phone without accessing its contents — it simply listens to the signals your phone voluntarily broadcasts.
Every pair of Bluetooth earbuds has a unique MAC address that it broadcasts while paired to your phone. Even when audio is not playing, the earbuds maintain an active Bluetooth connection that emits a detectable signal. Because most people use the same earbuds every day, this becomes a stable identifier — more reliable than a phone number, which can change.
Apple Watch, Fitbit, Garmin, and other wearables maintain constant Bluetooth connections to nearby phones. Each device has a unique Bluetooth identifier. Because people rarely change their watch, this identifier persists for years — a more stable tracking signal than a phone, which might be replaced annually.
Modern vehicles emit wireless signals from multiple subsystems: the infotainment system (Bluetooth and Wi-Fi), the tire pressure monitoring system (TPMS sensors in each wheel transmit wirelessly), the keyless entry system (RFID), and any built-in Wi-Fi hotspot. Each of these systems broadcasts identifiers that are unique to your specific vehicle.
Pet microchips use passive RFID technology — they do not have batteries and only transmit when energized by a close-range reader. SignalTrace's product materials list pet microchips among the signals it can detect. O'Horo's assessment is blunt: pet microchips are RFID tags operating on very low frequencies and are "usually only readable at a distance of centimeters." His theory is that Leonardo's marketing actually refers to Wi-Fi and Bluetooth-enabled pet collars, which do broadcast at detectable range — not to implanted chips.
The same analysis undercuts the tire-pressure claim. O'Horo found that flat-panel antennas of the type SignalTrace uses cannot pick up the frequencies most common tire pressure sensors operate on. He also notes that devices do not broadcast identifiers continuously and transmit across multiple channels, so a single roadside radio has to catch the right signal at the right moment on the right channel.
Where that leaves things. Several items on Leonardo's list appear to be marketing reach rather than demonstrated capability, and it is worth saying so plainly. But the core of the system does not depend on them. Wi-Fi and Bluetooth scanning is real, it works at roadside range, and O'Horo points out that some Flock cameras already have it. Your phone, earbuds and watch are the part that holds up.
RFID-enabled badges and access cards emit signals when near a reader. If you carry your work badge in your car — clipped to a visor, sitting on the dashboard, or in your pocket — it becomes part of your electronic fingerprint. This means your employer's access card could be used to identify you on your commute without your employer or you being aware.
SignalTrace does not identify you by any single device. Its value to law enforcement is in the combination. The system's algorithms analyze which devices repeatedly appear together at the same time and location, and associates that cluster of devices with a license plate.
Consider what your car broadcasts on a typical commute: your iPhone (Bluetooth identifier A), your AirPods (Bluetooth identifier B), your Apple Watch (Bluetooth identifier C), your car's infotainment system (Bluetooth identifier D), your car's four TPMS sensors (identifiers E, F, G, H), and your work badge (RFID identifier I). That combination of nine identifiers appearing together at the same camera, at the same time, associated with the same license plate, creates a fingerprint that is effectively unique to you.
Now imagine that fingerprint appearing across dozens of cameras over weeks and months. SignalTrace builds a pattern: these nine devices travel together on weekdays between 7:45 AM and 8:30 AM, passing cameras on the route between a residential neighborhood and a commercial district. On weekends, the same fingerprint appears near a grocery store, a gym, and a park. Over time, the system knows not just where your car has been — it knows your routine.
The critical shift: License plate readers have always tracked cars. SignalTrace tracks people. If you lend your car to your spouse, the system knows it is a different person driving because the device fingerprint changed — different phone, different watch, different earbuds. If you rent a car on vacation, the system can still identify you by your personal device cluster, even though the license plate is different. The fingerprint follows the person, not the vehicle.
SignalTrace operates in what privacy advocates describe as a legal gray zone. License plate readers have generally been upheld by courts as capturing information visible in public — your license plate is displayed on the outside of your car, visible to anyone. The legal framework that permits plate readers has been extended, without significant judicial review, to the collection of wireless signals that your devices broadcast in public space.
The argument is familiar: if your phone broadcasts a Bluetooth signal in public, you have no reasonable expectation of privacy in that signal. It is the same logic applied to license plates — if it is visible (or detectable) in public, it is fair game.
Privacy advocates counter that the aggregation of this data — combining plate numbers with device identifiers across thousands of cameras over months — creates a surveillance capability that is qualitatively different from a single observation in public. Knowing that a car passed one camera once is not the same as knowing every route a person drives, who rides with them, where they stop, and how often they travel together. The Supreme Court recognized this distinction in Carpenter v. United States (2018) regarding cell phone location data, but that ruling has not yet been applied to license plate reader networks or device fingerprinting.
Until a court rules otherwise, SignalTrace operates without a warrant requirement.
SignalTrace is a product of Leonardo US Cyber and Security Solutions, the American subsidiary of Leonardo S.p.A., an Italian aerospace and defense conglomerate. Leonardo is one of the largest defense contractors in Europe, with approximately 53,000 employees and revenues exceeding 15 billion euros annually. The company manufactures helicopters, radar systems, naval electronics, and cybersecurity products for military and government clients worldwide.
In the United States, Leonardo operates through its ELSAG division, which has been selling automatic license plate reader systems to law enforcement for over a decade. SignalTrace is marketed as an upgrade to existing ELSAG camera installations — agencies that already use Leonardo's plate readers can add SignalTrace sensors to their existing infrastructure.
Leonardo received a patent for the technology underlying SignalTrace in 2024. The product was previously marketed under the name "EOC Plus" before being rebranded. According to Leonardo's statements, SignalTrace is in the early stages of adoption with a limited number of law enforcement deployments, and the company has indicated that interest is growing beyond law enforcement into other sectors.
There is now a documented deployment. Security researcher Ryan O'Horo identified several SignalTrace installations in Oxon Hill, Maryland, operated by the Prince George's County Police Department. As far as O'Horo is aware, these are the only real-world SignalTrace deployments to date — a finding echoed by reporting in The Conversation in August 2026.
That single confirmed site is worth holding onto. This is not a network already blanketing the country; it is one police department's early installation. The reason to pay attention is not that SignalTrace is everywhere, but that it bolts onto plate-reader infrastructure that already is.
SignalTrace does not exist in isolation. It operates alongside the existing license plate reader infrastructure that has expanded rapidly across the United States. Flock Safety, the largest ALPR company in the country, operates cameras in over 6,000 communities. Other companies, including Motorola Solutions (which acquired Vigilant Solutions), operate competing networks.
Together, these systems have created a nationwide surveillance grid that records the movements of millions of vehicles daily. SignalTrace adds a new layer to this grid — one that transforms it from tracking cars to tracking the people inside them.
The ACLU's "Get the Flock Out" campaign has been working to raise awareness about license plate reader surveillance and advocate for restrictions on how the data is used. The campaign has succeeded in several communities that have voted to remove or restrict Flock cameras. SignalTrace represents an escalation that the campaign had not yet anticipated when it began.
1 Turn off Bluetooth when driving. This is the single most effective defense. Without Bluetooth, your phone, earbuds, and smartwatch stop broadcasting the identifiers that SignalTrace collects. iPhone: Settings → Bluetooth → Off (use Settings, not Control Center — Control Center only disconnects devices without fully turning Bluetooth off). Android: Settings → Connections → Bluetooth → Off. Turning off Bluetooth also disconnects your car's hands-free calling and audio streaming.
2 Turn off Wi-Fi when driving. Your phone scans for Wi-Fi networks even when not connected, broadcasting probe requests that contain identifiable information. iPhone: Settings → Wi-Fi → Off. Android: Settings → Connections → Wi-Fi → Off.
3 Use a Faraday bag for devices you are not actively using. A Faraday bag blocks all wireless signals — Bluetooth, Wi-Fi, cellular, RFID, and NFC. Placing your work badge, spare phone, or other devices in a Faraday bag while driving eliminates their signal contribution to your electronic fingerprint. Available online for $15-30.
4 Check if your community has Flock or ELSAG cameras. The DeFlock project maintains a crowdsourced map of known license plate reader locations at maps.deflock.org. If cameras exist in your area, they may already be collecting plate data — and could be upgraded to SignalTrace in the future.
5 Support legislative efforts to regulate surveillance technology. The ACLU's "Get the Flock Out" campaign advocates for restrictions on license plate reader use and data retention. Contact your local representatives and ask whether your community has approved the use of ALPR technology and under what policies the data is stored, shared, and deleted.
6 Understand what you cannot disable. Your car's tire pressure monitoring system (TPMS) is federally mandated and cannot be legally disabled. Each TPMS sensor broadcasts a unique identifier wirelessly. Your car's keyless entry system also broadcasts RFID signals. These vehicle-level identifiers are part of your electronic fingerprint regardless of what you do with your personal devices.
License plate cameras were sold to communities as tools to find stolen cars and track Amber Alerts. SignalTrace reveals what the infrastructure was always capable of becoming: a system that identifies not just where cars travel, but who is inside them, who rides with them, where they stop, and how they live their daily lives. Your phone, your watch, your earbuds, your work badge, and your dog's microchip are all part of the fingerprint. The question is no longer whether you are being tracked. It is whether anyone is watching.
SignalTrace collects device signals as you drive. Data brokers sell your name, address, phone, and personal information to anyone willing to pay. You cannot control roadside cameras, but you can send legal CCPA deletion demands to the 1,493 data brokers that hold your personal data. Reduce your digital footprint everywhere you can. $9.95/month.
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