Here is the example the vendor itself uses to sell the product. “While 70 cars in 100 may contain iPhones, only one will have an iPhone 13rev2, an Audi radio, a pair of Bose headphones, a Garmin sports watch, a key finder, and the license plate ABC-1234.” That sentence is on Leonardo’s own product page for SignalTrace, a system that bolts phone and wearable detection onto the license plate readers already mounted on American roadsides. Your Android phone, your watch and your earbuds are the components of the fingerprint.
What SignalTrace Actually Collects
Leonardo markets SignalTrace, formerly called EOC Plus, to US law enforcement as an add-on to its ELSAG plate reader line. The company’s description is straightforward: sensors placed at collection sites pick up the signals that fitness trackers, smartwatches, RFID tags and phones broadcast into the air, and correlate them with plate reads where a camera is present. In Leonardo’s words, “SignalTrace creates an electronic fingerprint for groups of the signals that the system determines are frequently emitted together.”
The output is stored on a server and can be queried later. Leonardo’s feature list says the system lets police “recognize a specific vehicle included in an electronic signature, without the license plate number”, reveals signatures that frequently travel together in order to spot convoys, and — this is the line worth pausing on — that “SignalTrace is effective in off-road areas such as in subways and malls”. It also states the system works with or without a plate reader at every site, which the company frames as wider coverage at lower deployment cost.
Read that back as a consumer rather than a procurement officer. A technology sold as an enhancement to roadside plate cameras is explicitly marketed as working indoors, on foot, where there are no cars and no license plates at all.
The Privacy Claim, and What It Leaves Out
Leonardo is direct about its privacy position. Its page says the system “does not decrypt or read the contents of the devices or their communications”, compares itself to plate readers capturing plate numbers rather than driver information, and says data simply sits until an investigator makes a request. Leonardo’s explanatory sheet says SignalTrace “does not identify people” and that it “only collects electronic signatures”, according to Nicole M. Bennett, a Ph.D. candidate in geography at Indiana University who examined the system for The Conversation.
All of that can be true and still miss the point. Nothing about the claim rests on the signal containing a name, because the identification happens afterwards, by joining. As Bennett puts it: “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.” A signature that keeps showing up next to a car registered to one person, or outside one address, stops being anonymous in any meaningful sense — and Leonardo’s own product copy says the sensors collect “electronic communication patterns and identities of consumer electronics”.
There is a second claim buried in the marketing that deserves scrutiny: that the system works because your specific mix of devices is rare. That is a description of a fingerprint, not of anonymity. The whole commercial value proposition depends on your device cluster being distinguishable from everyone else’s.
Where It Stands, and Where the Law Is
This is not yet routine policing. Bennett’s assessment is that “SignalTrace is a tested and marketed capability, but not yet an established police practice”, noting a report of several units installed in Oxon Hill, Maryland, and the predecessor technology appearing on a New York state contract price list.
The legal position is unsettled. The Supreme Court’s Carpenter decision established a reasonable expectation of privacy in the record of a person’s physical movements, and its June 2026 Chatrie ruling held that obtaining location data is a Fourth Amendment search. But Chatrie concerned records held by a company; SignalTrace concerns signals a device is broadcasting into open air. Whether collecting those counts as a search has not been decided.
What an Android User Can Actually Do
Not much, and it is worth being honest about that rather than offering false comfort. Modern Android randomizes Wi-Fi MAC addresses per network by default, and Bluetooth LE uses rotating private addresses, which makes single-device tracking harder than it was a decade ago. But Leonardo’s stated method is not tracking one identifier — it is recognising a recurring combination of nearby devices, and neither Leonardo nor any independent researcher has published how the system performs against randomization. There is no public testing at all.
The realistic mitigations are the blunt ones: turn Bluetooth and Wi-Fi scanning off when you are not using them, and check Settings > Location > Location services on Pixel and Samsung devices, where Wi-Fi scanning and Bluetooth scanning can each be disabled independently of the radios themselves. That reduces what your phone emits — though note the Bluetooth toggle governs scanning rather than broadcasting, so it is a partial measure at best. It does not stop your smartwatch or your earbuds, and it does nothing about the people sitting next to you — which, given that the system works on clusters, is the part you cannot control at all.
Sources: Leonardo ELSAG SignalTrace product page, Nicole M. Bennett, The Conversation
