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self-study / Criminal Law

Feb. 12, 2018

Drone Searches: A New Frontier for the Fourth Amendment

Recreational and commercial drone use has skyrocketed since the United States Congress' mandate to the Federal Aviation Administration (FAA) in 2012 to safely integrate drones into the national airspace. As a result, the FAA has loosened regulations, making it easier to operate drones commercially. See 14 CFR Part 107. Commercial drone applications include monitoring agriculture, broadcasting sporting events, oil and gas exploration, telecommunication uses and topographic aerial imaging and mapping. The global market for commercial drones or "unmanned aerial vehicles" (UAVs) is estimated to be worth at least $127.3 billion.

Not only are drones seeing increased commercial usage, but a growing number of government agencies are also turning to drones to assist with law enforcement and public safety. Drones can provide better access and improved safety in potentially dangerous situations. Firefighters have used drones to track forest fires. Local police departments have used drones to surveil property and assist in arresting suspects. A North Dakota sheriff's department requisitioned a drone from the U.S. Border Patrol to monitor a suspect in a standoff over trespassing cattle. See State v. Brossart, 2012 WL 10716031 at *2 (D.N.D.).

Increasing drone use in commerce and public safety will undoubtedly lead to increased privacy claims against both state actors and private individuals and companies. Legally, two basic regimes operate to protect individual privacy rights: (1) traditional tort claims, which may be used to protect people from non-governmental actors; and (2) the Fourth Amendment to the Constitution, which protects the public from governmental invasions of privacy. This article considers the latter regime and, specifically, the interplay between the Fourth Amendment and drone use in law enforcement surveillance.


The Fourth Amendment protects private citizens from unreasonable searches and seizures by the government. The amendment reflects "a choice that our society should be one in which citizens 'dwell in reasonable security and freedom from surveillance.'" California v. Ciraolo, 476 U.S. 207, 217 (1986).

This Fourth Amendment provides, in relevant part, that "the right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated." The touchstone of Fourth Amendment analysis is whether a "search" occurred. Except in limited circumstances, warrantless searches violate the Fourth Amendment and evidence collected during the search cannot be admitted in criminal proceedings. See Weeks v. United States, 232 U.S. 383 (1914).

In determining whether a "search" has occurred, the United States Supreme Court employs two tests: the "common law trespass test" (property-based approach) and the "reasonable expectation of privacy test" (privacy-rights approach). The common law trespass test focuses on whether there was a physical intrusion upon a constitutionally-protected area in order to obtain information. United States v. Jones, 565 U.S. 400, 404-405 (2012). The prototypical example under this test is a warrantless physical search of a home's interior. Kyllo v. Unites States, 533 U.S. 27, 28 (2010). In addition, the home's "curtilage" - such as the porch or other areas immediately surrounding a house - also typically receives Fourth Amendment protection. Florida v. Jardines, 569 U.S. 1, 7 (2013). However, areas beyond the curtilage - known as "open fields" - are not usually afforded protection. Oliver v. United States, 466 U.S. 170, 179 (1984).

Courts relied solely on the property-based approach until about 50 years ago when advances in technology required a similar evolution in Fourth Amendment jurisprudence. These advances, such as electronic listening and recording devices, enabled law enforcement to conduct highly intrusive surveillance without any physical presence on protected property. As a result, a new Fourth Amendment framework was needed. The Supreme Court responded with the reasonable expectation of privacy test, which reflected a shift from property rights to privacy rights.

Under this second test, whether someone has a reasonable expectation of privacy involves two inquiries: (1) whether the individual manifested a subjective expectation of privacy; and (2) whether society is willing to recognize that expectation as reasonable. Katz v. United States, 389 U.S. 347 349 (1967). While the first inquiry is typically straightforward, the second inquiry is not always clear. Societal expectations concerning physical intrusion into one's home or vehicle have had decades to take shape but the clay is far from dry regarding whether and to what extent society deems drone surveillance "reasonable."

For this reason, the drone technological revolution will present courts with unique Fourth Amendment issues. Recognizing that the Supreme Court has not yet decided a case involving drone surveillance and the Fourth Amendment, we have attempted to address the constitutionality of certain drone use by law enforcement through the following hypotheticals.

For purposes of the following hypotheticals, we have assumed that the law enforcement agencies conducting drone surveillance operations have obtained appropriate Certificates of Waiver or Authorization from the FAA and are not prohibited by local legislatures from conducting warrantless drone surveillance operations.


A law enforcement agency receives a tip that the defendant is engaged in human trafficking. Officers use a drone to follow the defendant's van to his property, where three hooded, bound individuals are unloaded from the rear of the van into the house. Tracking the defendant's car with a drone would not implicate the property-rights approach because there was no physical invasion of a constitutionally-protected area, such as the home's interior. Nor was there a "search" under the privacy-rights test because the defendant does not have a reasonable expectation of privacy while traveling in public. In United States v. Knotts, 460 U.S. 276, 281-82 (1983), the Supreme Court observed that a "person traveling in an automobile on public thoroughfares has no reasonable expectation of privacy in his movements from one place to another." Therefore, the government's drone surveillance and tracking of the defendant's car in public areas would likely survive a Fourth Amendment challenge.

Acting on an anonymous tip that the defendant is growing marijuana on his property, which is surrounded by a fence, officers fly a drone over the area at an elevation of approximately 400 feet. Using the drone's built-in camera, the officers take several photos of the property, which reveal that the defendant has extensive fields of marijuana growing in his backyard. This aerial surveillance would not likely constitute a Fourth Amendment search because the marijuana plants were observable from navigable airspace. In California v. Ciraolo, 476 U.S. 207 (1986), the Supreme Court held that the warrantless aerial observation of a fenced-in backyard within curtilage of home was not unreasonable under the Fourth Amendment. The Court observed that "the Fourth Amendment simply does not require police traveling in the public airways at 1,000 feet to obtain a warrant to observe what is visible to the naked eye." Id. at 208. Similarly, in Florida v. Riley, 488 U.S. 445 (1989), the Supreme Court held that an officer's observation of the interior of a partially covered greenhouse in a residential backyard from a helicopter circling 400 feet above did not constitute a search under the Fourth Amendment.


Suspecting that the defendant is operating a drug lab in his home, police fly a micro drone through a partially open basement floor window in the rear of the house where the drone captures images of chemical products and equipment commonly used in a drug manufacture. Flying a drone into a home without a warrant is very likely to constitute a search under the Fourth Amendment because such conduct involves a physical trespass. The so-called "plain sight" doctrine allows officers to look through windows when in a public place, such as the front door of a home, without first obtaining a warrant. United States v. Hersh, 464 F.2d 228, 230 (9th Cir. 1972). However, the Supreme Court has held that the "core" of the Fourth Amendment is the right to retreat into one's home and, therefore, law enforcement officers may not enter "into a man's office or home" to secretly observe or listen without a warrant. Silverman v. United States, 365 U.S. 505, 512 (1961). Therefore, the police's physical intrusion upon the defendant's home with a drone-whether such conduct meets the technical definition of a trespass or not under local law-would indisputably constitute a search under the Fourth Amendment.

Hovering over the defendant's house, police use a thermal-imaging device mounted to a drone to observe the activities taking place in the house. Provided that the device was not in general public use, this would likely constitute a search under the Fourth Amendment. In Kyllo v. United States, 533 U.S. 27 (2001), the Supreme Court held that using a thermal-imaging device to observe a suspect in his home constituted a search under the Fourth Amendment. Important to the Court's determination was the fact that the imaging technology was not in general public use and it allowed the police to obtain information about the home's interior that otherwise could not have been obtained without a physical intrusion. See Kyllo, 533 U.S. at 34.


Hovering over the defendant's automobile, police use a thermal-imaging device mounted to a drone to observe the activities taking place in the defendant's vehicle. Again, assuming that the thermal-imaging device has not become established in general public use, this may or may not constitute a search under the Fourth Amendment. Because the reasonableness of the privacy expectation is strongest within the home, law enforcement could argue that this use of a sense-enhancing device on a drone does not constitute a Fourth Amendment search because the defendant lacks a reasonable expectation of privacy in his automobile. Also relevant is the location of the automobile at the time of the observation. If the automobile was in the defendant's driveway, the defendant would have stronger grounds to argue that a search occurred. Alternately, if the defendant was parked in a public place, such as a commercial parking lot, law enforcement could argue that a search did not occur because the observation took place in a public area, where the defendant lacked a reasonable expectation of privacy.

Law enforcement uses a set of drones at an altitude of 400 feet to continuously monitor the movements of the defendant in a string of armed robberies over the course of several weeks. This drone surveillance may constitute a search under the Fourth Amendment. In United States v. Jones, 565 U.S. 400 (2012), the Supreme Court observed that the continuous visual monitoring of a suspect by a large team of agents would not likely constitute a search under the Fourth Amendment. However, the Court acknowledged that achieving the same result through electronic means without a warrant - even without a physical trespass - may constitute an unconstitutional invasion of privacy. The Court noted that the nature of the offense committed and the duration of the monitoring are factors that may affect whether such non-trespassory surveillance would be constitutional. However, the Court was unwilling to "grapple with these 'vexing problems,'" and left resolution of this question for another day. See Jones, 565 U.S. at 412.


It's only a matter of time before the Supreme Court will have to grapple with the vexing constitutional issues raised in the above hypotheticals. When it does, its focus will likely be on whether the defendant had a reasonable expectation of privacy in the information collected. However, in time, the proliferation of drone technology will alter how courts apply the Fourth Amendment. Indeed, Justice Sotomayor foreshadowed this outcome in her concurring opinion in United States v. Jones by suggesting that a fundamentally different approach may be necessary in the "digital age." See Jones, 565 U.S. at 413-418. Whatever novel approach the Court may develop to protect privacy in the digital age while preserving the Fourth Amendment's traditional check on governmental power will undoubtedly be influenced by the impact the drone revolution is expected to have on society.


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