The prospect of drone use in domestic surveillance operations has engendered considerable debate among Americans of various political ideologies. Opponents of drone surveillance have complained that the use of unmanned aircraft on American soil infringes upon fundamental privacy interests and the ability to freely associate with others. Some are specifically concerned about the possibility of turning military technology inward to surveil American citizens. Proponents have responded by emphasizing their potential benefits, which may include protecting public safety, patrolling our nation's borders, and investigating and enforcing environmental and criminal law violations. The tension between security and privacy interests is not new, but has been heightened by the explosion of surveillance technology in recent decades. Police officers who were once relegated to naked eye observations may soon have, or in some cases already possess, the capability to see through walls or track an individual's movements from the sky. One might question, then: What is the proper balance between the necessity of the government to keep people safe and the privacy needs of individuals? As some polls suggest, while the public supports drone usage in certain circumstances, they are less enthusiastic about using them as part of routine law enforcement activity. The Fourth Amendment to the United States Constitution safeguards Americans' privacy and prevents excessive government intrusion by prohibiting "unreasonable searches and seizures." Courts have long grappled with how to apply the text of this 18 th century provision to 20 th century technologies. Although the Supreme Court has the final say in the interpretation of the Fourth Amendment and other constitutional safeguards, Congress and, in many cases, the President are free to institute more stringent restrictions upon government surveillance operations. This report first explores the potential uses of drones in the domestic sphere by federal, state, and local governments. It then surveys current Fourth Amendment jurisprudence, including cases surrounding privacy in the home, privacy in public spaces, location tracking, manned aerial surveillance, and those involving the national border. Next, it considers how existing jurisprudence may inform current and proposed drone uses. It then describes the various legislative measures introduced in the 113 th Congress to address the legal and policy issues surrounding drones. Finally, it briefly identifies several alternative approaches that may constrain the potential scope of drone surveillance. Drones, also known as unmanned aerial vehicles (UAVs), are aircraft that do not carry a human operator and are capable of flight under remote control or autonomous programming. An unmanned aircraft system (UAS) is the entire system, including the aircraft, digital network, and personnel on the ground. Drones can range from the size of an insect—sometimes called nano drones or micro UAVs—to the size of a traditional jet. Drones are perhaps most commonly recognized from their missions abroad, including to target and kill suspected members of Al Qaeda and related groups, but they might be used for a variety of other purposes, including for both commercial and law enforcement activities within the United States. In fact, the FAA predicted that 30,000 unmanned aircraft could be flying in U.S. skies in less than 20 years. One reason for this expansion has been a push by Congress for a faster integration of UAVs into U.S. airspace. Most recently, as part of the FAA Modernization and Reform Act of 2012, Congress mandated that the Federal Aviation Administration (FAA) "develop a comprehensive plan to safely accelerate the integration of civil unmanned aircraft systems into the national airspace system." This plan shall provide for integration of UAVs by September 2015. Drones have been employed domestically by federal, state, and local governments in a range of circumstances. The Department of Homeland Security (DHS) uses them to police the nation's borders to deter unlawful border crossings by unauthorized aliens, criminals, and terrorists, and to detect and interdict the smuggling of weapons, drugs, and other contraband into the country. Within DHS, Customs and Border Protection's (CBP's) Office of Air and Marine (OAM) has flown missions to support federal and state agencies such as the Federal Bureau of Investigation (FBI), the Department of Defense (DOD), Immigration and Customs Enforcement (ICE), the U.S. Secret Service, and the Texas Rangers. According to a recent disclosure by the FAA, several local police departments, state and private colleges, and small cities and towns have also received FAA Certificates of Authorization (COAs) to fly unmanned aircraft domestically. Recently, a police force in North Dakota conducted the nation's first drone-assisted arrest. DHS, in conjunction with local law enforcement agencies, has been testing drone capabilities in a host of other situations including detecting radiation, monitoring a hostage situation, tracking a gun tossed by a fleeing suspect, firefighting, and finding missing persons. Currently, drones can be outfitted with high-powered cameras, thermal imaging devices, license plate readers, and laser radar (LADAR). In the near future, law enforcement organizations might seek to outfit drones with facial recognition or soft biometric recognition, which can recognize and track individuals based on attributes such as height, age, gender, and skin color. As explained below, the relative sophistication of drones contrasted with traditional surveillance technology may influence a court's decision whether domestic drone use is lawful under the Fourth Amendment. The Fourth Amendment's story is one of continuity and change. Core values such as privacy and protection from excessive and arbitrary government intrusion are always within its sweep. A continuing question, though, is how the demands of its protection apply to an ever-changing society in which new and pervasive forms of technology are increasingly common. Although there are numerous rules and exceptions throughout the Supreme Court's Fourth Amendment jurisprudence, this section will explore those most pertinent to domestic drone use. In short, the Fourth Amendment regulates when, where, and how the government may conduct searches and seizures. The Amendment provides, in relevant part: "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 Fourth Amendment does not apply to all government acts, but only to those that constitute a search. So when does government monitoring constitute a Fourth Amendment "search" for which a warrant is generally required? Initially, courts' assessment focused on the specific area being investigated. Consider the 1928 case Olmstead v. United State s . There, the Supreme Court held that police wiretaps of the defendant's home telephone did not constitute a Fourth Amendment search because the police did not trespass onto Olmstead's property to intercept his conversation. The Court's thinking at the time was that if the person's home, tangible property, or papers were not physically invaded, then no search in the constitutional sense occurred. Almost 40 years later, the Court shifted focus from property to privacy interests. In Katz v. United States , decided in 1967, the Court held that an FBI agent's use of a bug to listen to the private conversations of Mr. Katz while in a telephone booth violated his Fourth Amendment rights. Although he was in a public telephone booth and there was no physical invasion, the Court noted that what a person "seeks to preserve private, even in an area accessible to the public, may be constitutionally protected." One of the modern Fourth Amendment tests relied upon by courts in assessing whether government monitoring constitutes a "search" derives from Justice Harlan's concurrence in Katz . It considers whether the person has a subjective expectation of privacy in the area to be searched and whether society is prepared to deem that expectation reasonable. Although the Court said in Katz that the Fourth Amendment "protects people not places," Justice Harlan noted that determining what "protection it affords people ... requires reference to a ' place .'" And as Justice Scalia observed when writing for a majority of the Court in United States v. Jones , a Fourth Amendment search occurs, "at a minimum," where "the Government obtains information by physically intruding on a constitutionally protected area." The majority in Jones indicated that the reasonable expectation of privacy test was never intended to replace the property-based approach used in earlier cases, but merely augment it. So where do individuals enjoy the most Fourth Amendment protection? The least? Why does the location dictate the level of protection? And how does technology affect society's expectation of privacy? When analyzing domestic drone use under the Fourth Amendment, a reviewing court may be informed by cases surrounding privacy in the home, privacy in public spaces, location tracking, manned aerial surveillance, those involving the national border, and warrantless searches under the special needs doctrine. The home has always held a central place in American life, and remains the area accorded the greatest Fourth Amendment protection. The Fourth Amendment protects this zone of privacy by ensuring that "the right of the people to be secure in their ... houses ... against unreasonable search and seizure, shall not be violated[.]" In most instances, the Supreme Court has rigorously adhered to this safeguard. For instance, although police officers may make a warrantless arrest of an individual for a felony offense committed in public, they may not step inside his home without a warrant, barring any recognized exception. In addition to a physical entry and search of the home, police are likewise prohibited from using certain technology to pierce this zone of privacy. In Kyllo v. United States , government agents used a thermal-imaging device to determine heat patterns inside the home of Danny Kyllo. The Court began with the presumption that a warrantless search of a home is unreasonable. Ultimately, the Court protected this "realm of guaranteed privacy" by holding that obtaining information about the inside of a home that could not otherwise be obtained except by entering the home, through the use of technology not in "general public use," is a "search" covered by the Fourth Amendment. The home, however, does not provide an absolute shield against government surveillance.