Hundreds of Chinese-manufactured drones have been detected in restricted airspace over Washington, D.C., in recent months, a trend that national security agencies fear could become a new means for foreign espionage. The recreational drones made by Chinese company DJI, which are designed with “geofencing” restrictions to keep them out of sensitive locations, are being manipulated by users with simple workarounds to fly over no-go zones around the nation’s capital. Federal officials and drone industry experts have delivered classified briefings to the Senate Homeland Security, Commerce and Intelligence committees on the development, three people privy to the meetings said. A spokesperson...