Owning a carbon monoxide alarm is only half the job. The National Institute of Standards and Technology reports that the National Fire Protection Association recommends installing detectors on every floor of the home and in a central location outside each room where people sleep, following the manufacturer's instructions for your model.

Carbon monoxide is a gas produced by incomplete combustion, and NIST says it can seep from broken or misused heating systems. Faulty stoves or furnaces, and vehicles or portable generators run indoors, are all potential sources. The gas cannot be seen or smelled, which is why NIST calls detectors a critical last line of defense.

Detectors measure the gas in parts per million and sound off when enough is present for long enough to become a problem, according to NIST. Carbon monoxide at 70 ppm detected over a few hours will trigger an alarm. The goal is to give people time to get out before symptoms such as nausea, headache or loss of consciousness set in.

Portable generators deserve special care. NIST notes they can produce more than a hundred times the carbon monoxide of a car exhaust, and per the CDC they should never run indoors or within 6.1 meters (20 feet) of an open window, door or vent.

Sensors do not last forever, and the lifetime varies by manufacturer, NIST says. Detectors that meet the newest U.S. standards will signal when they have reached the end of their useful life and need to be replaced.