How do you tell there is CO in the air without a detector quickly??PLEASE HELP!!?

Jeez, this isn't an easy one. Carbon monoxide isn't detectable by the olfactory nerves (your sense of smell). Is there a 24-hour Walgreens/Walmart/something in your area? You can usually get a cheap CO detector, and if the place is close enough to home, it wouldn't take too long to fetch one. It's either that or stay up and constantly check everyone throughout the night.