The drone turned slowly with a loud buzzing sound, red and blue lights flashing, and hit me right in the eyes with a spotlight. "Security has been notified," boomed a smooth voice from the aircraft's twin loudspeakers. Startup Aptonomy thinks this experience can keep intruders out of factories, warehouses, and other facilities more cheaply than human guards can and more effectively than cameras and alarms. I received the drone security guard treatment in a demonstration at the company's testing area on Treasure Island, an old naval base in San Francisco Bay. Cofounder Mihail Pivtoraiko says his drones will be ready to go on patrol next year.