The Parrot A.R. Drone can maintain stable flight at an altitude of up to 20 feet, and a maximum altitude of up to 160 feet.
More sophisticated drones can fly higher and for longer, in a more stable fashion.
For example, protesters in Warsaw used a spy drone last month to see what police were doing. As diydrones.com notes:
People tend to assume that UAVs will be used by the police to keep watch on us, but as … video, taken by a RoboKopter of riots in Warsaw, shows, they can equally be used by citizens to keep tabs on the police. No need to wait for the local news to send a helicopter to get the aerial scene of a demonstration, just Do It Yourself!
Here is the video of the police shot by the Polish protesters:
(Here’s what the RoboKopter drone used by the Polish protesters looks like.)
For information on building your own drone, start here.
Disclaimer: The FAA apparently considers do-it-yourself drones to be legal. We don’t know whether there are any Department of Homeland Security or other regulations or laws prohibiting flying your own spy drone.Consult with a representative of all appropriate Federal, state, county and local agencies to determine whether or not you may fly your own drone.