Drones do amazing things. Today, they are racing, surveying crops and performing inspections. In the near future, they may be delivering stuff right to your home. But most of the time, they need someone to fly them. Drones that fly themselves, or autonomous drones, are another story. There are autonomous drones that can fly over large open spaces, using GPS and other sensors to cover a particular route, but flying through small spaces without crashing is much more challenging. Vijay Kumar’s lab at the University of Pennsylvania has developed a series of small quadcopter drones that can fly through a window by themselves. Using just an on-board camera, some sensors and a computer chip, the little machines zip through the air, sensing what is around them. When the drone spies a small gap in a window, it automatically knows how to position itself in space, judge the size of the opening, and fly through, even turning sideways to navigate a space tilted at 45 or 90-degrees. It is no small feat of engineering to get them to do this. In fact, it took the lab six years to figure it all out. Some of the applications for this ability are obvious: Inspecting hard-to-reach spots, search and rescue, and perhaps, more ominously, surveillance and spying.