A device can be borrowed or left in a car. A roadside sensor could capture someone standing nearby. Even a correct match between a device and a vehicle does not establish who carried it on a particular day.
Still, a pattern can direct police attention. Leonardo says SignalTrace is designed to develop leads. Leads influence which records officers request and whose movements receive further scrutiny. By the time an investigator attaches a name, the inferred association has already shaped the inquiry.
A study in the journal Proceedings of the National Academy of Sciences illustrates the power of relational inference. Researchers followed 94 participants using phones that recorded Bluetooth proximity and calling patterns. They found that patterns of behavior could accurately classify 95 percent of reciprocally reported friendships, with proximity outside work and during off-hours playing an important role in distinguishing friends from other people who regularly encountered one another.
SignalTrace uses a different method, and no independent study has shown comparable performance. The research nonetheless demonstrates that repeated proximity can reveal social ties.
This matters at a protest, for example. A person might come to police attention because their device repeatedly appeared near a group under investigation. The inference would arise from the company they kept, rather than an act attributed to that person.
When anonymous signals become identifying
What SignalTrace shows is a broader change in surveillance practice. Investigators may no longer need to begin with a known person or vehicle. Instead, they can begin with recurring patterns of movement and proximity, then use other records to identify the people connected to them.
That distinction matters because an electronic signature can become identifying without containing a name. A phone detected beside the same devices over time may reveal a relationship before the police know who owns it.
SignalTrace therefore raises a question that existing rules for license plate readers does not fully answer: How should the law treat systems that identify people indirectly through patterns and associations that their devices create?
Nicole M. Bennett is a PhD candidate in geography and assistant director at the Center for Refugee Studies at Indiana University.
This article is republished from The Conversation under a Creative Commons license. Read the original article.
