Smoke detector... the bad air quality or just a fluke?

I think David and I both have whiplash from being woken up from a deep sleep (I mean like jumping straight up out of bed!!!) by our smoke detector at 3:00AM and again at 6:15AM this morning.

We ran downstairs, searching everywhere for any signs off smoke and immediately found it odd that the smoke detector downstairs didn't go off, only the one upstairs.

We were stumped.

We just changed the batteries upon moving in last month and tested them all and it definitely was not that "dead battery" warning beep we had heard for a few days... this thing was actually going off!

The *only* thing we could think of is the bad air quality because of all the fires in our area - we sleep with our windows open at night and a big fan that brings air in from outside. Could it really be that? Maybe it was just some nearby smoke... but at 3:00AM? People don't BBQ at 3:00AM!

We are changing the battery again today, just to be sure it's working properly...