Ars Technica has a lengthy and interesting piece on Blue Jay, a Twitter live feed scanner intended for use by law enforcement officers, from a company with connections deep inside the US intelligence bureaucracy. From Ars:

. . . the "Law Enforcement Twitter Crime Scanner," which provides
real-time, geo-fenced access to every single public tweet so that local
police can keep tabs on #gunfire, #meth, and #protest (yes, those are
real examples) in their communities. BlueJay is the product of
BrightPlanet, whose tagline is "Deep Web Intelligence" and whose
board is populated with people like
Admiral John Poindexter of
Total Information Awareness infamy.
BlueJay allows users to enter a set of Twitter accounts, keywords,
and locations to scan for within 25-mile geofences (BlueJay users can
create up to five such fences), then it returns all matching tweets in
real-time. If the tweets come with GPS locations, they are plotted on a
map. The product can also export databases of up to 100,000 matching
tweets at a time.