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Detector doesn't give a chirp about logic


I GOT OUTSMARTED by a smoke detector recently. It happened when I was checking the batteries on the household detectors, a duty I am supposed to perform about once a year.

I usually end up doing it after one of the smoke detectors starts "chirping," indicating that it has a low battery. In this case, I did it after my wife had started "suggesting" that since we were going to put a Christmas tree and other flammable holiday decorations our house, it would be good idea to make sure our fire alarm system was functioning.

Checking the smoke detectors is a pretty low-skill operation, so I felt qualified to undertake it. I picked up a couple of new, 9-volt alkaline batteries, I got out the stepladder, and I flexed the index finger on my right hand.

My plan was simple. Position the stepladder under a smoke detector. Climb the ladder. Use the recently flexed finger to punch the test button on smoke detector. Then, either try not to fall off the ladder when the device emitted an ear-piercing screech, or if there was no screech, try not to fall off the ladder while snapping in a replacement battery.

When I installed the smoke detectors in our house many years ago, I put them in the recommended locations, either in the middle of a ceiling, or high on a wall away from corners. As I climbed the ladder, it seemed like the house had grown over the years. The ceilings sure seemed to be getting higher.

Two of the three smoke detectors were in fine voice, emitting blasts that rivaled the power of Kate Smith belting out "God Bless America." But when I punched the test button of the third smoke detector, it gave out a puny little peep.

I snapped a fresh battery into place, punched the test button, and braced myself for noise. Instead of an authoritative blast, the device made a feeble clicking sound. I tried to make things right by employing my two favorite repair techniques, pounding on the device and swearing at it. When they failed, I had to go fetch the power screwdriver and remove the troubled smoke detector from its perch.

I carried it into the family room. There, the smoke detector and I had a get-acquainted session. I examined its innards and snapped another fresh battery into the unit. Once again it refused to sound a strong alarm.

I was clueless. Seeking insight, I read about smoke detectors in "The Way Things Work," David Macaulay's cleverly illustrated guide to the workings of machines. I bought this book several years ago thinking I would give it to our kids so they could learn something. Instead, I kept the book for myself and find I regularly need Macaulay's child-level explanations of machinery.

According to the book, the smoke detector contained a chamber in which a low electrical current flowed through the air. When smoke entered the chamber, less current flowed and a microchip in the device responded to the drop in current by sounding the smoke alarm.

I closed the book and smiled. I still didn't have a clue why this smoke detector was misbehaving, but now I understood smoke-detector theory.

The smoke detector seemed to appreciate that I had taken the time to learn about its heritage. With the new alkaline battery in it, the device still hardly made a peep.

So I put the old alkaline battery back in the device and the alarm sounded perfectly. This didn't make any sense. It didn't seem to have anything to do with smoke-detector theory. But for some reason the detector worked with an old battery, not a new one. I didn't fight it. Instead, I climbed back up the ladder and reattached the smoke detector, powered by its old battery, to the wall. Then I went back to family room, stretched out in my easy chair and switched on the TV and got ready to watch the Ravens-Colts football game.

As soon as I got comfortable, that smoke detector started acting up. It began chirping, claiming it wanted a new battery. Yet when I had given it a new battery, it had refused to work. Chirp. Chirp. Chirp. What I had here was a smart-aleck smoke detector.

I tried to ignore it, but couldn't. Instead, I replaced it. I hurried over to the neighborhood hardware store and bought a new smoke detector.

I learned that there are all kinds of sophisticated detectors in the world today. There are smoke detectors that you can hook up to your electrical wiring, like a light. There are devices that detect both smoke and dangerous levels of carbon monoxide. There is even a device being developed by a "combustion researcher" at Purdue University that recognizes the "uncontrolled" flames of a fire and triggers an alarm, yet remains calm when it "sees" the civilized flickings of dinner-table candles. Fireplaces, however, give the detector fits and the researcher is working on that.

I read about these shrewd smoke detectors but didn't consider buying one. After being outfoxed by one smart-aleck smoke detector, I wanted its replacement to be plain, compliant, and downright simple.

Pub Date: 12/05/98

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