Answer: Radar

Although now ubiquitous, the microwave oven was once an expensive curiosity that was discovered entirely by accident. In 1945, Percy Spencer, an American engineer, was working on an active radar set and stumbled upon the food-heating properties of microwave radiation. In the course of working on the machine, he noticed that the Mr. Goodbar chocolate bar in his pocket had started melting in an unusual fashion.

He conducted further investigation with other food stuffs. The first food ever purposely cooked by microwave radiation was, fittingly enough, popcorn. He followed the popcorn with an egg, which exploded rather dramatically as it was heated from the inside out. After the initial experiments, he built a metal box to serve as a Faraday cage for the radiation and fed microwave power from a magnetron into the box. Food placed inside the metal box rose rapidly in temperature, confirming his hypothesis.

The first commercial microwave ovens were introduced in 1947. Dubbed the “Radarange”, they were almost six feet tall, weighed 750 pounds, pulled down three kilowatts of power, and retailed for $5,000 (roughly $57,000 in today’s money). Thankfully, in the intervening decades, prices and sizes have plummeted and a more effective microwave oven can be had for a fraction of the cost.