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Public video survdllance is changing the way police fight crime and terrorism. This was especially clear in the aftermath of the Boston Marathon bombing when law enforcement found images of the two suspects by analyzing surveillance images gathered by numerous public and private cameras. Such after-the-fact video surveillance was equally crucial to identifying the culprits behind the 2005 London subway bombing. But the rise of camera surveillance, as well as the emergence of drone-based video monitoring and GPS-tracking methods, not only provides an important boon for law enforcement, but also raises a challenge for constitutional law: As police gain the ability to technologically monitor individuals' public movements and activities, does the Fourth Amendment's protection against "unreasonable searches"place any hurdles in thdr way ?
In the 2012 case, United States v. Jones, five justices, in two separate concurrences, signaled that it does-at least when the monitoring becomes too intense or prolonged. Their suggestion, however, raises two significant problems. First, it provides no principled basis for marking the point at which public survdllance morphs from a means by which police monitor public space into a Fourth Amendment "search. " Under the "mosaic theory " embraced by the D.C. Circuit, such surveillance becomes a search only when it captures enough data points from an individual's public life to construct a detailed picture (or "mosaic") of her movements and associations. But how detailed may such a picture be before it is too detailed ? Do police engage in a search simply by watching someone continuously, even if they do so without drones, GPS units, or other advanced technology ? Second, the concurring opinions do not explain why the Fourth Amendment, if it does cover public surveillance of this kind, does not also cover the information-collecting police do when they simply watch a pedestrian or a driver. As Justice Scalia wrote in Jones, "Th[e] Court has to date not deviated from the understanding that mere visual observation does not constitute a search. " But if police collect the same information from watching a driver as they do from tracking him with GPS technology, why would thdr watching not also be a search ?
This Article proposes a solution to each of these challenges by offering a two- part definition...