The Mysterious Beeping Noise

A few nights ago, I heard a little "beep" in the middle of the night, most likely a smoke alarm running out of battery.  I decided to ignore it for a while, and it stopped.  It happened again a few nights later when I was vomiting all night during a rough bout of flu/food poisoning.

Then last night, even in a Nyquil induced coma, I heard it again and it woke me up.  Apparently, it also irritates the dog because I heard the beep, then heard a commotion in Dash's room, then heard Dash slowly sneaking up the stairs.  I've always said that I'm never worried about intruders because our stairs are so creaky, you can't sneak up on us, but it was a little scary because Dash was creeping very slowly.  I woke Jon up, and I went to put Dash away while Jon stood in the hall listening for the beep.

Dash gets put back in his room, and I go upstairs to help Jon listen for the beep.  We hear it again, then hear a commotion in Dash's room, then hear Dash's paw land outside of his room and he runs up the stairs.  The beep must really irritate him to the point he gets on top of his cage, jumps over his railing and lands on the outside of his room.  We spent another 10 minutes or so getting closer and closer to the beep, and locking Dash into his actual cage, before finding it and taking the battery out.  Of course, it still beeps one more time, like some possessed beeping demon.  Then, it gives up.

Here's a video I found applicable to this situation:
Phoebe and the Smoke Alarm