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Abstract

In Carpenter v. United States, the Supreme Court held that sufficiently lengthy surveillance of a person’s location was a search that presumptively required a warrant. This holding, the Court wrote, was an application of Katz v. United States’s battle cry that the Fourth Amendment “protects people, not places.”

Unfortunately, that battle cry is increasingly part of the problem. It was suited to Carpenter because it concerned the surveillance of Timothy Carpenter’s movement over 127 days. But police are increasingly supplementing long-term tracking of particular suspects with comparatively short-term tracking of whoever happens to occupy a particular swath of space during a particular span of time. Worryingly, this latter, place-based kind of surveillance seems to sidestep Carpenter’s person-centered rationale, even though it plausibly implicates the values that animated that opinion.

This Article identifies the truth in that worry and suggests a conceptual and doctrinal response. Specifically, I argue for three intertwined propositions that illuminate and bridge the gap between place-based surveillance and person- based precedent. My focal example is geofencing queries.

First, I argue that geofencing queries are not warrant-requiring searches under Carpenter. This is because Carpenter embraces a conservative idea of privacy, according to which, a person’s location is not private but may sometimes reveal that which is. I argue we should not follow this idea and instead hold that persons have a reasonable expectation of privacy in their location, as such. This would entail that geofencing queries presumptively require a warrant.

Second, I argue that geofencing warrants present unique issues precisely because they search arbitrarily specified spaces and times. Analyses of these problems often compare geofencing warrants to Ybarra v. Illinois and all- person warrants, but the jurisprudence that stems from Maryland v. Garrison is more on point. It leads to what I call the public scene principle for judging the appropriate breadth of geofencing warrants.

Third, I argue that even though reverse-keyword searches like the one in People v. Seymour bear some similarities to geofencing queries, they are also crucially distinct in concerning intellectual rather than locational privacy. They should therefore be subject to greater judicial scrutiny.

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