The use of drones in American skies raises new questions about the value of privacy and the extent of government surveillance, according to a report released last week by the Congressional Research Service.
It is not clear how courts will apply constitutional privacy protections to drones, but the report notes that Congress could enact laws to restrict the ability of police to use the technology.
Domestic drones are now uncommon, but the Federal Aviation Administration has predicted that within 20 years, 30,000 commercial and government drones could be flying in U.S. skies.
Drones could also be equipped with other surveillance technologies to identify people or license plates.
"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," the researchers write.
A drone from Lockheed Martin called the "Stalker" can be recharged from the ground using a laser. The report predicts that in the future, drones could theoretically stay in the sky forever.
Analyzing past court cases, the researchers conclude that police would likely have to obtain a search warrant to use nano drones or heat sensing imaging to spy on people within their homes.
But the report writes that it is unclear how courts will treat drone surveillance of a person's backyard, swimming pool, deck or porch.
The Supreme Court has held that police do not need warrants to fly helicopters or airplanes over people's homes and gather evidence. The justices concluded that the areas were in public view and the people should have had limited expectations of privacy.
The courts could treat drones similarly to other aircraft or they may decide that they raise more serious privacy concerns. Drones can stay in the air longer than manned aircraft and can hover in one place, the researchers note.
"This capability may sway a court’s determination of whether certain types of warrant-less drone surveillance are compatible with the Fourth Amendment," the researchers write.
Lawmakers have introduced several bills this session to limit how police can use drones to gather information.
Rep. Austin Scott (R-Ga.) and Sen. Rand Paul (R-Ky.) introduced the Preserving Freedom from Unwarranted Surveillance Act to require that police obtain a warrant in most circumstances before using drones. Paul's version of the bill explicitly says evidence gathered without a warrant cannot be used in trial.
Rep. Ted Poe's (R-Texas) Preserving American Privacy Act would only allow police to use drones with a warrant and to investigate a felony.
Rep. Shelley Moore Capito (R-W.Va.) introduced the Famers Privacy Act to restrict the Environmental Protection Agency's ability to use drones to investigate environmental violations. Sen. Barbara Boxer (D-Calif.) filed an amendment to the 2012 farm bill that would limited the EPA to using drones only if it is more cost-effective than ground inspections, but the amendment was not adopted.