I have issues with being woken up at night. Usually it is by snoring, cat purring, cat sitting on my feet, raccoon invasions, windchimes, rocket launches etc.
Sunday night I was dreaming that I was working in some nebulous office space (I believe you have my stapler!) and there was an alarm going off. I gradually realized I had woken up but was still hearing the noise. At 5:30 in the morning! I don't know what it was. Car horn? Alarm? Siren? I checked outside and it seemed to be coming from the north end of the street. The HH and I burrowed our heads under the covers but could still hear it. Finally, after the longest 15-20 minutes, it stopped.
I am happy to say there was no school Monday so I was able to sleep late to compensate.