Dealing with drones is becoming a bigger problem as more and more people buy and fly them.
The FAA is trying figure how to track them - especially around airports.
Current radar systems can't do that.
The agency tested three drone tracking systems near DIA on Wednesday.
Some had wings, others had rotors. They sometimes flew at 400 feet just 3 miles from the airport -- in restricted airspace.
Radar at airports across the country can't track the tiny aircraft because of their size and low altitude. They could be disastrous if they got too close to a plane.
"We are trying to find out what kind of system best detects a drone under a variety of different conditions," FAA Spokesperson Ian Gregor said.
In Denver, there have been reports of drones uncomfortably close to planes 21 times just this year.
The drone detection systems have have been tested at two other airports so far.
The FAA hopes to complete its study by the end of 2017.
However, there's no way to tell how long it will be before airports install new systems capable of tracking them.