Had a near miss today. My wife and oldest son got back home from camp before me, and the carbon monoxide detector was going off. She called the fire department and they came and cleared the place, but something was off with my furnace (which I still have to figure out). They were measuring 150 ppm which could have been fatal if we stayed at the house last night.

Lesson learned. Make sure you have a carbon monoxide detector and check your batteries, it could save your life.