When people worry about drones, they worry that the information gathered by the little fliers will be stored forever as a blanket violation of Fourth Amendment protections—a warrantless search with wings. (That's what people in the US worry about, anyway. People in other countries worry that drones will kill them.)
Looks like drones are the least of the Fourth Amendment's worries. From Wired.com:
Transit authorities in cities across the country are quietly installing microphone-enabled surveillance systems on public buses that would give them the ability to record and store private conversations, according to documents obtained by a news outlet.
The systems are being installed in San Francisco, Baltimore, and other cities with funding from the Department of Homeland Security in some cases, according to the Daily, which obtained copies of contracts, procurement requests, specs and other documents.
The use of the equipment raises serious questions about eavesdropping without a warrant, particularly since recordings of passengers could be obtained and used by law enforcement agencies.
It also raises questions about security, since the IP audio-video systems can be accessed remotely via a built-in web server, and can be combined with GPS data to track the movement of buses and passengers throughout the city.
Cities with these "microphone-enabled surveillance systems" (some partially funded by Homeland Security) include San Francisco, California; Eugene, Oregon; Athens, Georgia; Traverse City, Michigan; Columbus, Ohio; Baltimore Maryland; and Hartford, Connecticut.