The Digital Dragnet: How SignalTrace Turns Your Phone Into a License Plate

OPINION: We need to talk about the inevitable weaponization of this 'richer tracking.' While the tech industry frames these tools as neutral investigative aids, the reality is that digital invisibility is a luxury. For precarious workers and marginalized drivers who cannot afford to scrub their digital footprints, these systems create a permanent, searchable record of their associations and movements.

As Ars Technica first reported, a new system called SignalTrace, marketed by the security company Leonardo, is designed to integrate with automatic license plate readers. The technology detects signals broadcast by consumer devices—such as smartphones and smartwatches—traveling within a vehicle. By recognizing groups of devices that regularly move together, SignalTrace can associate those electronic signatures with specific license plate records and time-stamped locations.

This capability allows investigators to search patterns even without a specific license plate number. If a device signal appears alongside a different car connected to an investigation, police can use previous associations to deduce the identity of the person carrying the device.

Leonardo has attempted to distance the technology from direct identification. An explanatory sheet from the company claims SignalTrace "does not identify people" and only collects "electronic signatures" from Bluetooth or radio frequency identification tags, asserting these must be corroborated through standard investigative methods.

However, the reporting highlights a critical flaw. Police can identify a person by linking a signal to a car registered to an individual or by tracking a signal's presence outside a specific home. This means individuals could be pulled into investigations based solely on where their device appeared and who they were near, regardless of whether they were initial suspects.

While not yet a universal practice, Ars Technica reports that devices have been installed in Oxon Hill, Maryland, and predecessor technology has appeared on an official New York state contract price list.

The risks are supported by broader research. Ars Technica cites a study in the journal Scientific Reports involving 1.5 million people, which found that just four time-and-place data points were sufficient to uniquely identify 95% of individuals.

Legal precedents are struggling to keep pace. The Supreme Court case *Carpenter v. United States* established a reasonable expectation of privacy regarding physical movement records. In the June 2026 decision *Chatrie v. United States*, the Court ruled that obtaining location data constitutes a Fourth Amendment search after police used anonymized records to identify bank robbery suspects. The Court noted that even short-term monitoring can expose family and political associations, though it remains undecided if the wireless signal collection used by SignalTrace falls under this protection.