Annual Probability of CO Detector Alarm at Home
~5%
Annual probability in US
About 5% of homes with CO detectors experience an alarm each year. Most are from malfunctioning furnaces or improper ventilation.
Carbon monoxide detectors activate in approximately 5% of homes that have them installed each year. While many activations are due to actual elevated CO levels (often from malfunctioning furnaces, blocked vents, or running vehicles in garages), some are false alarms from detector aging, extreme humidity, or proximity to fuel-burning appliances.
Every CO alarm should be taken seriously. Carbon monoxide is called the "silent killer" because it is colorless and odorless. At low concentrations (50 ppm), symptoms include headache and fatigue after 2-3 hours. At moderate levels (100 ppm), symptoms appear within 1-2 hours. At high levels (400+ ppm), life-threatening symptoms develop within 1-2 hours, and death can occur within 2-3 hours.
CO detectors are required in residences in 37 states plus DC. They should be installed on every level of the home, particularly near sleeping areas. Detectors should be replaced every 5-7 years (as sensors degrade over time) and tested monthly. The leading sources of home CO are gas furnaces and water heaters, gas stoves and ovens, fireplaces and wood stoves, attached garages with running vehicles, and portable generators.
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