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Make sure your smoke detector is ready

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Posted: Thursday, December 6, 2012 12:00 am

The “Ask a Builder” series is dedicated to answering some of the many questions Fairbanks residents have about building, energy and the many other parts of home life.

Once bulky and expensive, smoke detectors now come with a variety of handy features and at affordable prices. One should be placed in every sleeping area of your home, on every floor of your home, in stairways, in main hallways and in garages. Alarms should be placed on ceilings.

There are two primary types of smoke detectors for residential use: optical and ionization. Optical smoke detectors have a photoelectric sensor that activates when smoke alters the focus of a small beam of light. Optical smoke detectors are a good choice for placement in kitchens and bathrooms because they are less susceptible to false alarms triggered by cooking fumes or steam. On the downside, optical smoke detectors are somewhat slower to detect rapidly growing flash fires than ionization detectors.

Ionization detectors generally are a little cheaper than optical sensors. These detectors use a wee bit of a radioactive element that alters current between two electrodes when exposed to smoke. Ionization detectors are great at detecting flash fires that produce small smoke particles, but they can be more prone to false alarms.

Perhaps the best alarms are the ones that combine both optical and ionization detectors into a single unit. This way, you can get the best features of both technologies. Less common, but still available, are air-sampling detectors, which can be highly calibrated and programmed with multiple alarm thresholds.

Some models of smoke detectors also offer carbon dioxide and carbon monoxide detection — but be sure that the model you choose is labeled to monitor gas levels full time, even in the absence of fire. Some units will tell you when the battery is low, if there is an alarm, and the amount of CO or CO2 detected.

A word about batteries: They’re necessary. If your house was built recently and built to code, chances are your detectors are hard-wired with battery back-ups and interconnected so that if one unit triggers, all will sound. But even these units’ batteries need periodic changing to remain effective. A good rule of thumb is to replace batteries at least once per year. Again, some smoke detectors will make an audible chirp or announce when their batteries need changing.

Smoke detectors themselves should be replaced every eight or 10 years. So, if you have a yellowing hunk of plastic on your ceiling and you don’t know how old it is, this would be a good time to buy a new alarm. Newer alarms have a slimmer profile, are more efficient and offer more features. Test your alarms regularly to be sure they’re working and so you know what they sound like.

Finally, if you hear an alarm, don’t assume a false alarm — and this certainly applies to carbon monoxide detectors, too, since the source of the alarm might not be directly apparent.

Ask a Builder articles promote home awareness for the Cold Climate Housing Research Center. If you have a question, contact us at or 457-3454.

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