This winter I have had two sets of friends, both older couples, suffer from carbon monoxide poisoning. One of them died last week from her exposure; her husband is expected to recover.

My husband reacted in the most productive way imaginable: On his way home from work Friday, he stopped at Wal-mart and bought a new, battery-powered CO detector to replace the old one in our basement. (You can get one there for $20 to $60.) In the process of making that switch, he learned that our basement, which houses our furnace, is not the best place to install such a detector. It now hangs in the upstairs hallway that connects all three of our bedrooms.

I responded in what I hope is an equally productive way: By writing this blog entry.

Carbon monoxide, which can leak into the air when heating devices are improperly installed or poorly vented, is produced whenever fossil fuels are burned. It is colorless and taste-free and has no odor, which makes it impossible to detect without, well, a detector. It tends to sneak up on people and do damage, or even kill them, before they know they’re in trouble.

According to the most recent federal data (published in 2007, but reporting on the years 1999 to 2004), non-fire-related CO poisoning is implicated in the unintentional deaths of about 440 people in the U.S. each year. Obviously, many more of those deaths occur in the winter, when we’re closed up indoors and running devices to warm our homes.

(Last Thursday, a Maryland state legislator called for requiring CO detectors to be installed in all public schools in that state.)

Here’s the CDC’s advice for avoiding CO poisoning. Among the top tips: “Do install a battery-operated CO detector in your home and check or replace the battery when you change the time on your clocks each spring and fall. If the detector sounds leave your home immediately and call 911.”

Checking (and replacing, if necessary) your CO detector is the kind of thing we tend to put off. Don’t do that. Check yours as soon as you get home, will you?