Harmful gasses in my house? Any idea?

So.. last night a friend came over, and as soon as he came in he told us our house smelled like fog machine (which has a distinct smell, different from just burning wood or matches or cigarettes). We couldn't smell it last night, but just got up this morning and walk into the kitchen/livingroom area and yeah.. it smells like fog machine. My bird has been covered up in his cage all night in the livingroom and doesn't appear to be ill from whatever it is. It is very very faint, but it is there. No appliances are left on, no haziness in the rooms, just a slightly noticeable smell of fog machine.

Any ideas on what this might be? Anything I should be concerned about? Who should I give a call if it gets worse and needs to be checked out? Not incredibly concerned, as I said it's been present since at least last night and if it were harmful, I'd likely see something with the animals, but... don't want it to get worse, and no idea what could be causing it.

I think fog machine smells like stagnate water. You may look for water leaks or mold in your home, that could be causing the smell.

Fog machines vaporize Glycol, I doubt that you have any of that in your house. I would check your refrigerator for refrigerant leaks.

Ugh, just found it. Plugged in heat cable to see if it still worked and it was too close to some loose bedding. No burning, just heated up dust/bark. Got distracted and forgot to unplug it, and now feel like an idiot. I wired a fan and heat pad for a different incubator last night... and was worried it was from that, but absolutely no smell in the snake room... panic for a moment and think it is the heat lights I have on the cold garage rat tubs...nope, all good...walk back into kitchen, and there is the heat cable. /facepalm.