- Andrew G. Ferguson, Digital Rummaging, 101 Wash. U. L. Rev. 1473 (2024).
- Andrew G. Ferguson, Everything-Everywhere Searches, _ G.W. J. of L. & Tech. _ (forthcoming), available at SSRN (Feb. 17, 2025).
Advances in digital surveillance technologies have posed difficult questions for Fourth Amendment doctrine. For instance, does the government need a warrant to install cameras on poles along a street to monitor who enters and exits homes? What if the government wants a list of all cell phones near a robbery scene at the time of the crime? Is the answer different if the government wants several days of data, but only about one person? What if the data comes from an app developer like Waze (or your flashlight app) or a smart home device like an Alexa, rather than a cell phone provider?
The Supreme Court has begun to address these issues in cases like Riley (barring warrantless cell phone searches during arrest) and Carpenter (requiring warrants for long-term cell phone location data). But as Andrew G. Ferguson argues in two recent articles—Digital Rummaging and Everything-Everywhere Searches—Fourth Amendment doctrine has nonetheless not kept pace with the scale of digital surveillance. In a turn to history that may prove particularly persuasive to constitutional originalists, Ferguson argues that the Founding generation’s objections to “rummaging” through general warrants provide an appropriate guiding principle for constraining surveillance in the digital age.
Ferguson warns that existing doctrinal focus on “reasonable expectations of privacy” and “trespass” may perversely encourage mass surveillance: “by searching everyone and everything at the same time, police can elide the traditional threshold search and seizure questions because it is not clear what expectations anyone has under such continuous surveillance or even when the search occurs.” As an antidote, Ferguson revives the Founding Era’s concern with “rummaging.” In Digital Rummaging, he introduces the “rummaging principle,” traces its historical roots, defines a “rummaging test” for courts, and applies that test to smart home data and long-term digital pole camera surveillance. In Everything-Everywhere Searches, he extends the rummaging principle to geofence warrants. Both articles merit close reading.
Ferguson traces the “rummaging principle” to the Founding generation’s deep mistrust of “government agents rummaging around homes, property, and papers.” Rooted in opposition to general warrants and writs of assistance, this principle has long served as a background constraint in existing Fourth Amendment doctrine. As the Supreme Court has observed, the Fourth Amendment was a direct response to these colonial-era abuses, “which allowed British officers to rummage through homes in an unrestrained search for evidence of criminal activity” (emphasis in Ferguson). Drawing on early sources, like Wilkes v. Wood and Entick v. Carrington, Ferguson shows how terms like “rummage,” “rifle,” and “ransack” captured the Founders’ fear of unchecked searches. While the Supreme Court has generally overlooked rummaging in defining what counts as a search, recent cases involving digital technology in policing, like Carpenter, have begun to resuscitate interest in this inquiry.
Building on this history, Ferguson distills the rummaging principle into a modern “rummaging test” constraining digital policing under the Fourth Amendment. He argues that courts should ask whether a contested search involves “(1) arbitrary enforcement of police power; (2) overreaching exploratory expansions of initially justified searches; (3) intrusions into constitutionally secured interests (e.g., homes, persons, papers, effects, location); or (4) exposure of private details as a form of political or social control.” These inquiries, Ferguson explains, align with the core harms that the Fourth Amendment was meant to prevent. Arbitrary enforcement occurs when unchecked police power leads to unreasonable interference with individuals or communities. Overreach happens when searches are too broad, such as using “probable cause pretext about one crime to search for other[s]” or sweeping innocent conduct or people up in investigations.
Intrusion refers to government efforts to access constitutionally protected spaces, people, or information. As Ferguson observes, protecting the home means safeguarding “the things that happen inside those four walls, not the walls themselves.” So too for people and, among other things, the information in their DNA. Finally, exposure involves the risk of revealing private information, recalling early privacy law concerns about the “privacies of life.” Government searches can create stigma that signals guilt to others and can become a powerful tool for social or political control.
Ferguson argues that this rummaging test can help determine both whether a “search” has occurred and whether a warrant, or other procedural or legal safeguards, makes that search reasonable. Ferguson also suggests that if a search causes significant enough rummaging harms, it may violate the Fourth Amendment even with a warrant.
The rummaging test clarifies decisions like Riley and Carpenter, which limited warrantless government conduct and “embraced—without necessarily acknowledging it—the principles behind the rummaging test.” It also casts doubt on older decisions, like Greenwood, in which the Supreme Court held that there is no Fourth Amendment protection for trash—an outcome Ferguson suggests fails to account for the harms of rummaging.
Turning to new forms of digital policing, Ferguson applies the rummaging test to smart home data and long-term pole cameras. Police typically use these tools based on mere hunches, hoping that rummaging through the data might turn up something useful. But if police can use these tools without a warrant, as prosecutors argue, it opens the door to arbitrary, overbroad, and deeply intrusive searches. Most of the information gathered would be “innocent, embarrassing, or irrelevant.” Smart home data may reveal details not otherwise “obtainable absent an entry into the home (if then),” while pole cameras could be deployed against disfavored individuals and entangle anyone with whom they socialize. Nonetheless, Ferguson suggests that with carefully crafted warrants—including “minimization requirements, time limits, or other considerations”—these tools might yet pass constitutional muster.
Finally, in Everything Everywhere Searches, Ferguson expands the rummaging test to digital surveillance that targets everyone’s data in hopes of generating a suspect list, or even just clues to the start of one. Ferguson focuses on geofencing, but similar mass queries arise in law enforcement use of consumer genetics data to generate leads by identifying genetic relatives of an unknown suspect, persistent aerial surveillance that records and stores data about everything that happens on city streets, facial recognition tools that can track or identify persons of interest, or tools like Shotspotter that are always listening and direct police to possible crime scenes where everyone present comes under suspicion. Ferguson identifies three characteristics these technologies: they are pervasive, capturing information in “widespread, comprehensive, and voluminous” ways; they are digital, enabling investigators to “search back in time, aggregate the data, and connect personal data points for new insights”; and they are indiscriminate, “collect[ing] information constantly against everyone, innocent, guilty, or anywhere in between.” These features often frustrate Fourth Amendment protection, especially when courts treat third-party data as beyond its scope.
Ferguson applies the rummaging test to geofence queries, where police ask companies like Google to identify all devices present in a specific area during a specific time. Police often use a geofence query when they have no suspect in mind, hoping that someone in the data will fit. Ferguson argues that warrantless geofence queries are classic rummaging—arbitrary, overbroad, and deeply intrusive. In this location data panopticon, “even just the potential of collection” could be chilling. Even with a warrant, problems remain, because of the inevitable involvement of private intermediaries.
Ferguson analyzes geofence warrants as currently conducted: authorized by courts, but mediated in a three-step process by Google. At Step One, Google scans its entire location database and returns anonymized data on all devices in the geofence—an overbroad search that sweeps in innocent people. Steps Two and Three narrow the pool and eventually identify individuals, but the initial dragnet remains constitutionally troubling. Ferguson warns that, even with these limits, “in terms of a grant of power, it is hard not to see the rhetorical parallels between geofence warrants and the general warrants that gave rise to the Fourth Amendment.” To be lawful, courts would need to impose a far more rigorous definition of particularity, and even then, such warrants might only “slightly alleviate” our concerns.
Ferguson’s expansive work on digital rummaging skillfully shows us one more way in which the doctrinal myopia on “expectations of privacy” or “trespass” can miss the real harms the Fourth Amendment was intended to prevent. His rummaging test offers a historically grounded lens for explaining the harms of big data searches that “invert the traditional investigative model.” This work invites fresh debate and legal challenges across a host of investigative methods, both well-established and new. Perhaps most controversially, Ferguson suggests that some surveillance practices may be so invasive that they should simply be off limits—warrant or not.
