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 are cheaper to build and fly than manned aircraft, making them more useful to the government for aerial surveillance. Some drones are the size of traditional jets but others — called “nano drones” — can be as small as an insect.

Drones could also be equipped with other surveillance technologies to identify people or license plates.