The liberty at stake here is freedom of movement without a permanent, searchable record. There's a meaningful difference between "a person can see you in public" and "a corporation logs your plate, location, and timestamp thousands of times a month and makes it queryable." The Supreme Court moved in this direction in Carpenter v. United States, when it ruled that accessing historical location records constitutes a search even when the individual data points were shared with a third party, because the whole is greater than the sum of its parts.
Some real-world examples of "the whole being greater than the sum of its parts":
- If your plate and another person's plate consistently show up at the same locations at the same times, that's evidence of a relationship. Now multiply that across everyone. You can map social networks, figure out who's meeting with who, identify affair partners, figure out who attends the same AA meeting every Tuesday.
- Regular trips to a mosque, a church, a union hall, a gun range, a protest staging area, a political campaign office. No single trip is meaningful, but the pattern over months tells you someone's affiliations and beliefs.
- Repeated visits to an oncology clinic, a methadone clinic, a fertility specialist, a psychiatrist's office. That's health information that would normally be protected under HIPAA if obtained through medical channels.
- When you leave for work, when you come home, what routes you take, when your house is empty. This is exactly the kind of information a stalker would want, and it's sitting in a database that (depending on the jurisdiction) may have minimal access controls.
The key point is that none of these individual observations are particularly sensitive. It's the longitudinal aggregation that transforms mundane location data into an intimate portrait of someone's life. And importantly, that portrait exists for essentially every driver, not just people under investigation.
You could argue that the 4th Amendment constrains state action, not corporate behavior. But it's not like Flock is collecting this data for some independent commercial purpose and the government occasionally subpoenas it. The product is government surveillance, just privatized. Outsourcing surveillance to a private contractor to avoid 4th Amendment scrutiny is arguably worse than the government doing it directly, because it bypasses the oversight mechanisms that keep the government in check (or at least, are supposed to do so).
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