We touch, hold, long-press or tap this symbol every day—even several times a day—but the power icon has become so ubiquitous that its meaning doesn't get a second thought. Where did it come from?
The line symbolizes the number one, YouTuber Lazy Game Reviews explains in his latest video. The half-circle is a zero, a reference to the binary "on/off" states. The line intersects the circle to communicate that this button won't cut power fully, but is a standby mode—a line inside a circle, or an empty circle, would turn on or shut down power completely.
You don't have to know anything about binary to understand the button's purpose, and that's the whole point.
As electronics and automobile import sales started to rise, the words "on" and "off" on power buttons were replaced with a icon that could be understood intuitively across languages. In 1973, the International Electrotechnical Commission added the power symbol to its collection of "graphical symbols for use on equipment," and it's stayed the same since.
The collection that birthed the power symbol became a universal code-book for many of the technology icons in use today. These simple, elegant drawings are our planet's modern hieroglyphics.