What should I watch for?

Household signs include:

stuffy air
excessive moisture on windows and walls
soot build-up around appliances and vents
a yellow flame in a natural gas appliance instead of blue
a pilot light that keeps going out

Personal symptoms include:

dizziness
burning eyes
headache
vomiting
nausea
loss of muscle control
fatigue

The severity of symptoms will vary, depending on the concentration and length of exposure as well as the general health of the victim. Since these symptoms match those of the flu and other common illnesses, carbon monoxide poisoning is often difficult to recognize.