Based on news reports, lawsuits, police and fire records, and research by advocacy groups, at least 36 people have been killed in the United States in such incidents since 2006, including seven in the past six months. Dozens of others have been injured, some left with brain damage.

The deaths of Ms. Penney and Mr. Livingston were all the more striking because of their accomplishments in academia and science. Before retiring to Florida, Ms. Penney was the first woman to serve permanently as chancellor of the University of Massachusetts Boston and held other leadership roles in the UMass and State University of New York systems. Mr. Livingston, an expert on magnets, spent decades as a researcher at General Electric and taught at the Massachusetts Institute of Technology. The couple collaborated on a book about Martha Wright, a women’s rights figure in the 1800s who was Mr. Livingston’s great-great-grandmother.

“These are very smart people,” Ms. Livingston said. “This kind of situation can happen to anybody.”

The National Highway Traffic Safety Administration, which oversees the auto industry, proposed a rule for keyless vehicles in 2011 mandating a one-second audible external warning to drivers to turn off the ignition. The rule would cost the auto industry $500,000 a year, according to an agency estimate. But after lobbying from the industry, the proposal has remained in limbo.

Asked recently for comment, the agency repeated earlier guidance, pointing consumers to a safety video about the use and potential dangers of keyless ignitions.

Some keyless models activate audible warnings or flashing lights inside or outside the car if the door is opened while the motor is running. The Toyota Avalon, for example, is designed to beep once internally and three times externally in such circumstances. But as the deaths of Ms. Penney and Mr. Livingston indicate, such alerts are not always adequate.