Some are as large and fast as commercial airplanes. Some are blimps that sit in the sky, surveying broad swaths of territory. Others flit around imperceptibly, like birds or insects, recording videos and landing themselves.

Unmanned aircraft have transformed the way the U.S. wages war, making it possible to gather unprecedented amounts of aerial imagery using nearly undetectable platforms and to strike at targets without putting pilots at risk. But it would be naive to assume drones will only be used to safeguard U.S. interests. As they continue to become smaller, cheaper and more
numerous, drones will become easier for hostile nations, and perhaps even terrorists, to get their hands on. To think otherwise would be to disregard the history of military technology. Many countries, including Israel, China and Iran, are developing, using and selling drones, and global spending on drones is expected to approach $100 billion over the next 10 years.

Should a terrorist group deploy a drone in the U.S., it could be very hard to detect. Drones can fly right over fences and walls and are invisible to traditional radar systems. Because they can be transported in the trunk of a car or in a backpack, they can be launched from virtually any publicly accessible spot.

We might also be worried about our own government, or private companies, using drones to peer into our lives. In 1986 the U.S. Supreme Court ruled that law-enforcement agencies could use a private plane to view otherwise hidden marijuana plants because the police observations were made from “public navigable airspace.” This may suggest that the government will enjoy broad latitude to use drones for surveillance.

Tightening access to drones is very difficult. The core information technologies used in small drones—extremely small video cameras, chips to process video and high-speed wireless communications systems—are routinely found in inexpensive consumer electronics.  

This does not mean that there is nothing we can do. Drones could be equipped with kill switches and hidden tracking software that could help disable or trace them if they go missing. A combination of domestic regulation and international nonproliferation efforts could reduce the possibility that drones would fall into the wrong hands. It may be possible to equip sensitive government buildings or areas with new systems to detect and, if appropriate, electromagnetically or kinetically engage low-flying incoming drones. Yet despite these efforts, in the future we will no longer have the luxury of assuming that the skies above us are free of pilotless machines.