During the month of August so far, at least six children in the United States have died of hyperthermia after being shut up in a car on a warm day.

Mark Pelletier, a master electrician and a technician for a Coca-Cola bottling plant in Minnesota, has invented a car alarm that he thinks could save some of the dozens of children who die this way each year.

“It’s a horrible death,” Mr. Pelletier said. “They wouldn’t let a criminal who has committed a heinous crime die in this way.”

Small children, because of their size, are especially susceptible to dehydration and heat stroke, said George Askew, a pediatrician and the executive director of Docs for Tots, an advocacy organization in Washington. A child can heat up as much as five times faster than an adult. Heat stroke can occur when the body’s internal temperature rises above 104 degrees Fahrenheit.

And the temperature in a closed car rises rapidly. According to a Web site on hyperthermia fatalities maintained by a professor at San Francisco State University (ggweather .com/heat/hyperthermia2004.htm), a car sitting in the sun on a 76-degree day can heat up to 100 degrees within a half-hour. “On a hot day in an unventilated car, an infant could become dehydrated in a very short time,” Dr. Askew said. Many carbound pets also perish every year from hyperthermia.

Sometimes children have been saved by passers-by who, by chance, saw them shut up in cars on warm days, leading some inventors to develop alarm systems that would call attention to the dangerous situation.

One of those is Mr. Pelletier, who after watching a television news report of a child’s death several years ago, decided to focus on the problem, approaching the automobile as he would a piece of industrial machinery. He came up with a programmable circuit board that turns on motion-detecting sensors when a closed-up car reaches a certain temperature (say, 88 degrees). If motion is detected, an alarm goes off.

More here.