We got downstairs, and I could tell it was coming from the bathroom. Our downstairs faucet isn't well-insulated, so it can occasionally freeze in 15 degree weather (like tonight). I'd turned on a heat lamp. That heat lamp had fallen off the clip, and was proceeding to scorch its way through the bottom of the sink cabinet.
I grabbed the plug to the heat lamp, and pulled it so hard the lamp flew back out of the cabinet, causing it to burst the filament (i.e. nice flash, no damage). There's now a two-inch wide scorched wood mark in the bottom of the cabinet. It's solely God's hand of protection that the cabinet didn't burst into flames.
There really wasn't even any smoke downstairs, so <mumble> even if I'd had the smoke detector working downstairs</mumble> it wouldn't have helped. I'm just glad that the dog had to go.