As a kid, twice I woke up from weird dreams of alarms and urgency and did a heart-pounding search until I found smoldering items in my parents house. One was a towel against a wall heater one floor down in a bathroom. The other was my baby brothers pillow which had fallen against a space heater in his room. Whew.
I had an electrician in because when I smelt heated plastic I tracked down a hot outlet cover. Old worn wiring was thisclose to igniting.
I had a gas guy in because of the smell coming from a valve by my hot water tank. He told me I shouldn't have been able to smell the gas, but it was so evident I had to do something about it. Yup - pinhole leak beside the pilot light.
A while back I stopped in the middle of a very pleasurable interaction with my Lady because I smelt scorched plastic. Turns out the candles placed around the room were causing the new air conditioner's casing to brown and bubble up. Moved some candles, then went back at it.
Years ago I tracked down yucky potatoes in the apartment next door - I had been left the keys to take care of the guys mail. Got to take care of his mess as well
Of course there was the time I found leaking coolant dripping onto the exhaust when driving the car - that stuff turned to steam and the smell was pretty nasty the way it caught in your chest. No one else in the car seemed to notice, though. Go figure.
If I smell something off in the house, I always track it down, no matter what time it is.