When the body temperature is high and spirits low, what kid wants an icy thermometer stuck in his mouth (or worse)? But that's been the only way to measure a Saturday—and every other night—fever since the little glass rod filled with mercury was invented back in 1714. Now, however, parents have an alternative: the Fever Scan.

The Scan is a three-inch plastic strip with heat-sensitive black bands that glow an iridescent green to indicate the temperature from 97° to 104°. You don't have to shake it, you can't break it and the reading takes only 15 seconds, not three minutes.

The magic in the strip is a liquid crystal similar to that used in digital watches and mood-stone rings. Extracted from either sheep's wool or pig fat, the crystals are highly sensitive to molecular changes in the body—which occur with fluctuations in temperature.

It took more than a crystal ball, of course, to see the profitable future in Fever Scan. Its creators—Marvin Kidd, 39, of Dayton, Ohio, and Winfried Schuberth, 38, a German who emigrated there—met while working in the special products division at National Cash Register. "NCR had experimented with liquid crystals, but nobody knew what to do with them," says Schuberth. When he and Kidd thought they had an answer in 1973, they left NCR and founded the American Thermometer Co. Another NCR employee, William Hultquist, 36, joined them a year later, and they moved from Kidd's basement to what had once been the factory of the famous Maxwell automobile in Dayton. The first product was a thermometer that stuck to the side of aquariums, a prototype for the current forehead model. When the mood-ring craze began to sweep the country in 1976, however, American Thermometer stopped everything else and boosted its staff from five to 85 to cash in.

Then the partners turned back to thermometers and since last March have sold two million of them. Fever Scan costs slightly less (list $2.29) and is more accurate than the mercury thermometer—among other plusses. "When I was a child and my mom grabbed a thermometer and told me to open up, I said: 'Ugh,' " Kidd recalls. "But I loved my mom putting her hand on my forehead. Now we're back to the mother's touch."

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