The sirens went off again the other night, only this time it was late evening instead of the middle of the night. I immediately got on Skype and started typing away to some friends in the city to see if they could hear them as well.
Much to my dismay, no one else could hear the sirens. When I considered how loud they were for us, I just assumed they were broadcast throughout the entire area. Apparently I was wrong. I still didn't have my problem solved. John guessed it had something to do with the impending storm, but that wouldn't explain why they sounded in the middle of the night a while back.
So, my mystery was still just that... a mystery. Until a German friend responded and gave me an answer! Apparently the sirens go off in your area when there is a fire. I don't remember hearing any fire engines racing by, but perhaps I was so intent on the sirens and the racing of my own heart that I didn't listen for anything else.
Case solved. Now my imagination can rest.