Shira just called to tell me about the Active Shooter in the DC Navy Yard.
A few moments later, I thought I heard a loudspeaker from outside. I cautiously opened my door and this is what heard:
Attention...all personnel are directed to shelter in place at this time...go to the nearest building and remain inside until the all clear has been announced...
I can't tell where the loudspeaker is positioned, so it might not be intended for the general population. Maybe I'm hearing a message from the nearby Fort Meyer or the Pentagon.
Either way, very spooky.
Update: with no special activity and no Arlington alert message, this was almost certainly a notification meant for Fort Meyer, the nearby base. Like I said, very spooky, but apparently, nothing to be alarmed about.