But the problem has not been solved. In 2010, 49 children died when they were left behind or inadvertently trapped in a parked car, a peak at the time. In 2018, 52 such deaths were recorded, according to data compiled by KidsAndCars.org.

“Education of caregivers is at an all-time high,” Ms. Fennell said, “so deaths shouldn’t be at an all-time high.”

Ms. Fennell has again asked Congress to act, with the Hot Cars Act of 2019. In addressing the House’s Consumer Protection and Commerce Subcommittee on May 23 about the bill, she said, “Once and for all we must reach an agreement that education alone will not and cannot put an end to these needless tragedies.”

The House bill, which is due to be introduced this month, is expected to require an audible warning if someone is in the back seat after the engine is turned off. Such technology is already standard on the Kia Telluride and Hyundai Santa Fe, providing an alert if ultrasonic sensors detect child or pet movement in the second and third row.

A Senate version of the bill was introduced on May 22, but it wouldn’t require an occupancy sensor. A warning system that alerts the driver if the rear door was opened before beginning a trip, for example, would most likely satisfy the requirements of the Senate bill. Unlike the Kia and Hyundai technology, these systems cannot detect the presence of a person or pet in the back seat.

The Alliance of Automobile Manufacturers is again calling only for more public awareness. The organization posted this statement regarding the new Hot Cars Act on its website:

“The loss of any life is tragic, and greater public awareness and vigilance are absolutely crucial to help save young lives, right now, this week. The alliance will carefully review any legislative proposals keeping in mind that fewer than 13 percent of new car buyers have a child 6 years old or younger. And with people keeping cars longer, it takes about two decades for a technology to reach all the passenger vehicles on our roads. Greater public awareness saves lives today.”

While Ms. Fennell has pushed for change over the past two decades, she remains optimistic. “I’m feeling much more bullish, because no one is running away from us,” she said. “For the first time ever, people are saying let’s get this done.”