Install carbon monoxide alarms on every level and outside sleeping areas
Added
Put battery-powered CO alarms (or plug-in/hard-wired units with battery backup) that meet the UL 2034 standard on every level of the home and outside sleeping areas. Interconnected alarms are best so they all sound together. Avoid kitchens and spots above fuel-burning appliances; test monthly and replace the unit when the maker says its life is up.
The result
Result: CPSC: install UL 2034 CO alarms on every level and outside sleeping areas; interconnected alarms are best. A CO alarm adds protection but does not replace proper appliance use and annual heating-system service.
Source
U.S. Consumer Product Safety Commission (CPSC) (opens the original source in a new tab). Check it for the latest numbers before you act.