Photo by Rick Geary

By now we’d all glow in the dark like big fireflies.

Dear Matthew Alice: Is it true that the smoke detector, installed by the builders of my condo in '79, has a radioactive element in it? If so, is it strong enough to be harmful in the corner of my bedroom? Yes, I know — why am I asking now, after 15 years! — Bill Cromwell, Mission Valley

If there were any radiation danger from ionization-type smoke detectors. Bill, by now we’d all glow in the dark like big fireflies. And photoelectric-style devices contain no radioactive elements. So no matter which type you have, your health has suffered more from 15 years of worry than from any leaky rays. An ionizing detector has a pill-sized, shielded bit of americium-241, which “ionizes” the air inside the device, completing an electrical circuit. Smoke particles disrupt the connection and trigger the alarm. (In photoelectrics, the smoke scatters a light beam.) And here it comes, the obligatory goofy-but-eye-opening comparison apparently required in every radiation story. If you snuggled under the covers with your ionizing alarm every night for a year, you’d be exposed to a tenth of the radiation dose (0.5 milligram) you’d receive on a round-trip plane flight from New York to L.A., according to the Nuclear Regulatory Commission. All consumer products contribute only 3 percent to the average person’s annual radiation exposure.

Consumers Union poked and pummeled ionizing detectors and imagined every possible ugly scenario while preparing their smoke-detector safety story for the January 1977 issue of Consumer Reports. As you might expect, they say your risk from fire is real; your risk from smoke detectors is virtually nonexistent, assuming you don’t eat one or stick the pellet up your nose. (A few years ago, a creative Canadian decided to commit suicide by cooking the radiation pellets from two smoke alarms in a kettle of onion soup. He ate a bowl or two each week for a month. If it eventually kills him, it could take years. Hope he doesn’t change his mind in the meantime.)

A few more detector tips. The photoelectrics are better at sensing a smoldering fire (the cigarette-in-the-sofa-cushions type); ionizing detectors are much better at sensing a blaze that emits little or no smoke. CU recommends you put both types in some rooms. And don’t throw a conked-out ionizing detector in the trash. It’s against the law. Mail it back to the manufacturer.