“a siren blaring on and off that I can only describe as sounding like an air raid siren”, Anyone Else Hear It?

Photo by PoPville flickr user Clif Burns

“Dear PoPville,

I live in Adams Morgan and for the past hour (since about 9:30am), there has been a siren blaring on and off that I can only describe as sounding like an air raid siren. It continued on and off until 11:15 or so. Does DC have a city-wide air raid siren system, and, if so, how are we supposed to know the difference between a test and an actual alert?”