The world's first autonomous indoor drone surveillance system has been developed by two European companies. The unmanned machine carries out its own patrol route through the corridors and rooms of the building it is monitoring, landing itself on a wireless charging pad whenever it runs low on power. A surveillance camera attached to the quadrocopter records and streams real-time footage and alerts human guards to any potential threats. The engineers behind the system claim building owners could replace hundreds of static cameras with a few drones, saving costs while keeping their property secure. The world's first autonomous indoor drone surveillance system (pictured) has been developed by two European drone companies'Drones work best in surveillance applications and are more cost effective,' said David Trillo, CEO of Spanish communications and drone technology developer Avansig, one of two companies working to create the new system.