The US Federal Aviation Administration says it is testing new technology that will hopefully detect drones flying close to airports.
The agency says a reliable system to track the flight of drones is essential for air safety.
Currently existing radar systems cannot pick up signals from drones due to their size and low altitude.
The FAA and the Department of Homeland Security have begun drone-detection research at Denver Airport.
Tests are being carried out at six airports over the next 18 months.
These are Atlantic City Airport, New York JFK, Eglin Air Force Base, Helsinki Airport, and Dallas-Ft. Worth.
The FAA warned flyers not to be alarmed if they spot drones close to the airport.
"Unmanned aircraft that enter the protected airspace around airports can pose a serious threat to safety. The FAA is working to evaluate new technologies for detecting unmanned aircraft near airports," it said in a statement.
"The FAA and Department of Homeland Security will be conducting research in the vicinity of Denver International Airport this week, which could result in people seeing small unmanned aircraft in that area."
Data will be collected under various weather conditions and other criteria and used to make recommendations for selecting drone-detection systems for airports nationwide.
