CO cannot be detected by human senses

Carbon monoxide is colorless and odorless, so people cannot reliably notice it without an alarm. The U.S. Fire Administration (USFA) identifies poorly operating or vented fuel-burning equipment and generators as possible sources. Headache, dizziness, nausea, and confusion can resemble other illnesses, so symptoms alone cannot confirm exposure. An alarm provides an early warning; it does not replace safe appliance use and maintenance.

Follow U.S. placement guidance and the device instructions

For U.S. homes, USFA recommends CO alarms on every level and in a central location outside each separate sleeping area. The U.S. Consumer Product Safety Commission (CPSC) also says to install alarms according to the manufacturer’s instructions and keep them from being covered by furniture or draperies. These are U.S. consumer recommendations. Check local building and electrical rules where you live, and select features such as battery backup or interconnection according to the applicable code and product specifications.

Testing, batteries, and replacement depend on the model

CPSC explains that a test button checks the circuitry, not the accuracy of the CO sensor; sensor life and replacement timing vary by model; use the date and instructions supplied with the actual device. A test button checks alarm operation and is not a measurement or calibration of carbon monoxide in the room. If an alarm sounds, do not stay inside to investigate. Get everyone outdoors to fresh air and contact local emergency services.

CPSC placement details and the chamber study's limits

The CPSC fact sheet says to follow the device instructions and avoid heating vents, places where furniture or draperies can cover the alarm, kitchens, and positions above fuel-burning appliances. A separate experiment introduced CO at the top, middle, and bottom of an eight-foot sealed chamber; concentrations eventually equalized. This challenges a simple rule that CO always sinks to the floor, but the experiment did not measure alarm response across rooms, doors, and airflow in an occupied home. Follow local rules and the actual alarm manual. If an alarm sounds or exposure is suspected, leave rather than investigate indoors and contact emergency services.

Sources and references: Carbon Monoxide Poisoning Prevention | U.S. Fire Administration / Carbon Monoxide Fact Sheet | U.S. Consumer Product Safety Commission / Should the Placement of Carbon Monoxide (CO) Detectors Be Influenced by CO’s Weight Relative to Air? | Journal of Emergency Medicine (Hampson, Courtney and Holm)