Think finding a reasonably priced smoke alarm that can also detect carbon monoxide fumes is a no-brainer? Think again. Product-testing giant Consumer Reports' latest assessment of carbon-monoxide and smoke alarms revealed that it's difficult to find one product to meet most homeowners' needs.

CR's test of 25 alarms, published in its November issue, showed that safety is far too complex. It noted, for example, that some smoke alarms that use ionization technology, while good at detecting fires that suddenly erupt, such as paper, were lousy at detecting smoldering fires, say, in a mattress. The opposite was true for photoelectric alarms.

Then there were models that used both technologies, giving homeowners a heads up on both kinds of fire, but failed to detect leaks of CO, a colorless, odorless gas that can cause brain damage or death. It's emitted from fuel-burning appliances, such as water heaters and furnaces.

The test also showed that those alarms that combined both fire and CO detection detected only one type of fire, and weren't always able to communicate with one another, should you have more than one alarm in your house. That's important, say, if there's fire or a CO leak in your basement while people are asleep upstairs. An alarm that senses smoke or gas broadcasts the alarm to other alarms in the house.

Though there are adapters that allow hard-wired models, those that run off a home's electrical system, to communicate with competitors' models, wireless models, that operate solely on battery, can only talk with alarms of the same brand, since manufacturers' use different frequencies. It's a problem that should be fixed, CR says.

With a little mixing and matching, however, CR says households can be safeguarded. Some models provided excellent protection and any of the units tested would be better than no alarm at all.

Read more about Consumer Reports test of smoke and carbon monoxide alarms online at consumerreports.org (subscription required).