Oregon law requires CO2 and smoke detectors in the home when a fuel-burning appliance is installed.
The law requires a CO2 detector within 15 feet of any bedroom or sleeping space. It also requires a smoke detector no farther than 15 feet from any bedroom, plus one in every bedroom.
Smoke and CO2 detectors can be in a common hallway as long as they are no farther than 15 feet from the doorway of any given bedroom.
In addition, you need a minimum of one detector on every floor of the living space.
They make smoke and CO2 combo units, and these can be placed in all locations for additional protection.