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In Birchfield v. North Dakota (2016), the Supreme Court broke new Fourth Amendment ground by establishing that law enforcement's collection of information can be cause for 'anxiety,' meriting constitutional protection, even if subsequent uses of the information are tightly restricted. This change is significant. While the Court has long recognized the reality that police cannot always be trusted to follow constitutional rules, Birchfield changes how that concern is implemented in Fourth Amendment law, and importantly, in a manner that acknowledges the new realities of data-driven policing. Beyond offering a careful reading of Birchfield, this Article has two goals. First, we compare Birchfield to two fixtures of Fourth Amendment law that likewise stem from distrust of state power: the warrant requirement and the exclusionary rule. Like traditional warrants, 'Birchfield warrants' have a prophylactic quality; they enable ex ante judicial supervision. But Birchfield warrants also go further than traditional warrants; they aim to anticipate--and preempt--disregard for the rules later on, not just to safeguard particularity in the immediate search or seizure. In this sense, Birchfield warrants do ex ante what the exclusionary rule does ex post: deter abuse. Second, we connect Birchfield's 'anti-anxiety' logic to two other areas of constitutional criminal procedure. The first are settings--speedy trial and double jeopardy cases, most notably--where the Court has recognized that potential uses of state power can provoke anxiety and, accordingly, require constitutional accommodation. We refer to this as the 'Sword of Damocles' problem. The second area is Miranda, which, like Birchfield, deals with a problem of 'closed-door' policing. In both Miranda and Birchfield, protective rules are necessary because law enforcement decisions happen in the dark--in Miranda, due to the realities of traditional custodial interrogation, and in Birchfield, because collected information simply disappears into a government vault. Birchfield is, in effect, the Court's first 'big data collection' case, having doctrinal implications for the seizure and use of any information-rich evidence, including support for Fourth Amendment use restrictions. In this sense, Birchfield is best understood as continuous with other recent jurisprudence--most notably, United States v. Jones and Riley v. California--in which the Supreme Court has revitalized the ideal of judicial supervision in the age of data-driven policing., I see the sword of Damocles is right above your head.--Lou Reed, Sword of Damocles (Sire Records 1992) INTRODUCTION The police, courts like to note, are engaged in the 'competitive [...]