Earlier this month, U.S. News & World Report ran the following headline: "Court Upholds Domestic Drone Use In Arrest Of American Citizen." The article goes on to explain that a man was arrested in North Dakota with air support from a Predator B drone on loan from the Department of Homeland Security. His attorney filed a motion to dismiss on the basis that local police had not secured a warrant to use a drone in his arrest. The court, understandably, denied the motion. As I and others have observed, the Fourth Amendment does not restrict the use of drones to assess whether a perpetrator is dangerous. It would only be implicated if, for instance, one person were followed around for a long time, or the entire population were placed under constant aerial surveillance. And even then the outcome of a challenge is uncertain.
The U.S. News & World Report story and others like it ran not because of a novel legal question, but because people are fascinated by drones. One of the reasons for this fascination, I think, is that we tend to associate drones with the military context. Indeed, the Predator B is a serious piece of military equipment---it just happens that a domestic agency owns a fleet of them.
I am aware of no ban on the domestic use of technology that originates in the military. Many local SWAT teams have armored tanks, for instance. And such a rule would mean we wouldn't be able to use technologies as central as radio or the Internet. But we do have a law that prohibits the "willful use[ of] any part of the Army or the Air Force as a posse comitatus or otherwise to execute the laws." The Posse Comitatus Act limits the use of federal military personnel (the Army and, since 1956, the Air Force) to enforce local law.
Now, a posse comitatus challenge to the North Dakota arrest would fail, if for no other reason than the Department of Homeland Security, which supplied the drone, falls outside of the Act. Moreover, subsequent amendments to the Act (courtesy of the wars on drugs and terrorism) permit "passive" military support in the form of intelligence sharing. But is this the right result? As domestic law enforcement gets greater and greater access to military-grade technology---whether because federal agencies loan it out, or it becomes cheap enough for local police to afford---do we not begin to run afoul of the spirit of posse comitatus? Presumably the purpose of this Reconstruction-era law was to curtail the use of overwhelming federal resources in local affairs.
Indeed, one need not look far to find articles addressing this very issue. I would add but the following: just as our fascination with robotics may finally catalyze changes to privacy law, perhaps our visceral reaction to drones and other robotic soldiers in our midst will occasion a reexamination of the scope of posse comitatus. We could imagine a claim that the technology used to apprehend an individual was, though not technically a search, grossly disproportionate to the alleged crime (here, cattle rustling). If so, might the Fourth Amendment might have a kind of posse, too?