New tech adds phone tracking to license plate readers, associating devices with identifiable cars
Skip to content
License plate readers like this one could soon be joined by sensors that detect phones inside passing cars.<br>Justin Sullivan/Getty Images
https://theconversation.com/new-tech-adds-phone-tracking-to-license-plate-readers-associating-devices-with-identifiable-cars-288876
https://theconversation.com/new-tech-adds-phone-tracking-to-license-plate-readers-associating-devices-with-identifiable-cars-288876
Link copied
Share article
Share article
Copy link
Bluesky
Messenger
X (Twitter)
Print article
Imagine that you share a ride to work with the same colleague most mornings. As it passes by a license plate reader, the camera records the car, which can be linked through vehicle records to its registered owner. Beside it, another sensor detects signals broadcast by devices traveling nearby, such as your phone and your colleague’s smartwatch.
After enough trips, software may treat some of those devices as a recurring electronic signature associated with the vehicle. Weeks later, one of the same device signals appears alongside a different car connected to an investigation. The signal itself may not contain its owner’s name, but its previous association with a known vehicle gives investigators another clue they can use to work out who was carrying the device.
SignalTrace, a system marketed by the security company Leonardo, is designed to work alongside automatic license plate readers. The company says it can recognize groups of consumer devices that regularly move together, then associate them with license plate records and time-stamped locations. The pattern can then be searched even when a police investigator does not know the plate number.
I am a researcher who studies the intersection of data governance, digital technologies and governments, including surveillance technologies. I see that SignalTrace could further shift how police conduct investigations, putting emphasis on people’s movements and associations before their identities are known.
SignalTrace is a tested and marketed capability, but not yet an established police practice. One report indicates that several of the devices are installed in Oxon Hill, Maryland, and the company’s predecessor technology appears on an official New York state contract price list.
License plate readers help police track vehicles – and raise significant privacy concerns.
A narrow definition of identification
Leonardo’s new explanatory sheet states that SignalTrace “does not identify people.” It says the system “only collects electronic signatures” from signals already being broadcast, such as Bluetooth or radio frequency identification tags. Those signatures, by themselves, do not disclose a person’s identity. The company says the output must be corroborated through ordinary investigative methods.
That description relies on a narrow meaning of identity, however. A sensor may not pull a legal name from a phone, but police could still work out who likely owns the device by linking its signal to other records. For example, the same signal might repeatedly appear with a car registered to one person, outside that person’s home, or alongside another device already connected to a known subject. That means a person could become part of an investigation because of where their device repeatedly appeared and who it appeared near, even if the police had no reason to suspect that person at the outset.
Leonardo’s SignalTrace product page says the system stores electronic fingerprints for later queries and can recognize a vehicle without seeing its license plate. A separate product sheet says the technology helps identify suspects through the mix of devices they carry. The patent behind the system describes targets that may be people or vehicles. It also describes searchable signatures that can be correlated with visual identifiers and used to track a target across locations.
SignalTrace may begin with a nameless pattern, but its value comes from recognizing that pattern again and connecting it to information that police already possess. Once an officer links a recurring signature to a license plate record or case file, the absence of a name in the original signal offers little protection.
A nameless identifier can still be personal
Federal privacy guidance does not limit identifying information to names. The National Institute of Standards and Technology defines personally identifiable information as data that can distinguish or trace a person’s identity, either alone or when combined with linkable information. The key question is whether data can single someone out and follow them over time.
Research on mobility data – records collected from people’s mobile devices indicating where they went – helps explain the risk. A study in the journal Scientific Reports examined 15 months of records covering 1.5 million people....