When Margaret A. Wilcox developed the car heater, she did it in an era where being a mechanical engineer was a rarity—and which was even more difficult for a woman. Every time you warm up your icy extremities behind the wheel on a cold winter day, you have Wilcox to thank.

Born in Chicago in 1838, Wilcox spend her life designing machines that were intended to make life a little easier. And in her late 20s, Wilcox discovered a problem: the few folks who actually rode and drove in railway cars—the only ‘cars’ available at the time—were suffering from icy fingers when it got cold. Technology back in the day was pretty rudimentary, with very little insulation or comfort.

Wilcox, then, started experimenting with a really cool idea. She figured that, since engines create a lot of heat, she could run a channel of air through the engine and then send it back into the rail cars. It was a pretty genius concept, one that hadn’t been considered before. And Wilcox received a for her idea in November of 1893.

It wasn’t an easy road, though. Wilcox had patented previous ideas—like a combination clothes-and-dishwasher that could tackle two washing tasks at once—but it was illegal for women to do so under their own name at the time. Wilcox had to file that previous patent under her husband’s name. But by 1893, women were allowed to file patents. So, she was able to receive full credit for her invention.

That said, not everyone loved the idea because it was still pretty rudimentary. Significantly, there was no way to regulate temperature. Riders were just subjected to an onslaught of hot engine air that would progressively get hotter the longer they rode. So, you could either have icy fingers or burning ones. It was up to you.

But Wilcox’s idea is still the basis for car heaters today, and it was the idea that engineers turned to when they were trying to regulate temperature in the automobile. Early cars were all exposed, with the first enclosed cars hitting the consumer market in 1907. Rudimentary heaters were installed as early as 1917, but it wasn’t until Ford started using Wilcox’s hot engine air design in 1929 that the cabin actually reached a noticeably warm temperature.

In most cases today, hot coolant from a vehicle’s engine is passed through a tube, which exchanges heat between the coolant and the cabin air. When you warm the air, it warms the cabin. And we now have a temperature control system that can blend the heated air with the cooler air outside to help create the most comfortable temperature possible.

Updated 3/4/22 with new details.