First: You should look for a carbon monoxide alarm that is listed to the October 1, 1998 UL 2034 Standard. It is the most recent standard developed with the assistance of the Consumer Products Safety Commission, Medical and Industry experts. The goal eliminates false alarms while protecting the public from fatal levels of Carbon Monoxide.
Second: If you expect young children, elderly adults or anyone with heart or respiratory conditions to be present, look for an alarm that has a two-stage alarm. One alarm set for LOW CO levels (50 to 70 ppm) and a HIGH CO alarm for levels over 100 ppm alarm.
Third: Look for an alarm that returns to normal after ventilation. Alarms that take hours to return to normal leave you unable determine if you ventilated properly leaving you at risk.
Fourth: Look for an alarm with peak CO alarm level memory. Without this invaluable feature first responders (Fire Department, Heating Contractor, Utility Company, etc.) consider many alarms false because the residence was ventilated and no measurable CO is present when they arrived.