The History of the Power Symbol: The International Standard Behind I, O, and ⏻

In the corner of a laptop or on a remote control, there’s often a symbol that looks like a circle with a line slightly overlapping it. Most people simply call it the “power button.” But when this symbol first appeared in an international standards document, its name wasn’t “power” at all — it was “stand-by.”^[1] Even today, the symbol printed on your television or computer is, strictly speaking, designed to indicate not a fully powered-off state, but a half-on one.

Hidden inside this seemingly trivial symbol are three overlapping stories: a numbering system, decades of debate inside international standards bodies, and a reality that still isn’t unified even after the standard was set. Despite pressing it several times a day, few people could explain where it actually comes from.

Why a Straight Line and a Circle?

The two shapes that make up the power symbol — a straight vertical line (I) and a round circle (O) — are actually numbers. The most basic way computers and electronic circuits represent signals is binary, a system that uses only two states. A state where electricity is flowing through a circuit is represented as 1, and a state where it isn’t is represented as 0.^[1] Flip a switch on, and the circuit connects so electricity flows (1); flip it off, and the circuit breaks so no electricity flows (0).

The power symbol is simply these two numbers rendered as pictures. The number 1 became a vertical line, and the number 0 became a circle.^[2] So if you look closely at a power button, what you’re actually looking at isn’t letters or pictures at all — it’s the binary digits 1 and 0, superimposed on each other. This method of turning numbers or letters into extremely simple pictures to convey meaning is called a pictogram. The same principle is at work in the human figure on a restroom sign or the running figure on an emergency exit sign — images drawn so that anyone can grasp the meaning without any accompanying text.

This idea itself wasn’t new. Early electronic devices often had the English words “ON” and “OFF” printed directly next to their switches. The problem surfaced once these devices started being sold across borders. If a washing machine made in France was exported to Germany or Japan, consumers there might not be able to read the English lettering. Engraving a different word for each language on every single switch was both costly and inefficient.^[2] What was needed was a symbol anyone could recognize regardless of language. The answer turned out to be a straight line and a circle, modeled on the numerals 1 and 0.

Around the same period, the same underlying problem was being tackled in several other fields — emergency exit signage, laundry care labels, road signs. Conveying meaning through pictures instead of words meant no translation was needed, and the symbols could be engraved even into extremely small spaces. That was an especially important advantage for parts like switches and buttons, which are often only a few millimeters across. The power symbol was one instance that emerged as this broader system of international pictograms took shape.

Officially an International Standard in 1973

This line-and-circle symbol first appeared in an official document in 1973, in the International Electrotechnical Commission’s (IEC) standard for “Graphical Symbols for Use on Equipment” — IEC 60417 (then designated IEC 417).^[3] The IEC, established in 1906, is the body that governs international standards in the electrical and electronics field, setting the rules manufacturers around the world follow when building products meant to cross borders.^[3] That said, records show that several manufacturers had already been using similar shapes informally even before the symbol appeared in the document, so it’s more accurate to treat 1973 as the moment an existing practice was formalized rather than the moment the symbol was invented.^[1]

IEC 60417 doesn’t contain just one power-related symbol. The symbol with only a vertical line (reference number 5007) indicates that power is fully connected, while the symbol with only a circle (reference number 5008) indicates that power is fully disconnected.^[4] Both symbols are still used separately today on certain electrical outlets and industrial switches.

The process behind the now-familiar symbol — a vertical line overlapping a circle — turns out to be surprisingly simple. The already-existing “on” symbol (the line) and “off” symbol (the circle) were simply layered on top of one another.^[1] But hidden within this combined symbol is a twist, which we’ll get to shortly.

The Combined Symbol Was Never Actually “Off”

A closer look at the IEC 60417 standard reveals something surprising. The symbol people today commonly call the “power button” — a line crossing through a circle — was originally registered under reference number 5009 as the “stand-by” symbol.^[4] According to the standard document’s definition, this symbol wasn’t created to represent a switch that turns a device fully off, but rather a switch or position that shifts the device into a low-power standby state.^[4] In other words, it was designed to represent exactly the state you’re in when you turn off a television with a remote: the screen goes dark, but the power cord is still drawing electricity.

There is a separate symbol for a single button that toggles between fully on and fully off. Registered under reference number 5010, it looks similar to the stand-by symbol, but its circle is unbroken and fully closed, with a line running vertically through the middle.^[4] Commonly rendered as the Unicode character ⏼, this symbol is typically used on switches that turn the power itself completely on or off — a circuit breaker on a wall outlet, for instance.

This distinction seems minor, but it actually matters quite a bit. On a photocopier, “stand-by” often means the device is fully powered on and ready to operate immediately, whereas on a computer or monitor, “stand-by” means a limited-function, low-power state that can take time to wake from.^[5] With the same word and the same symbol carrying entirely different meanings depending on the type of device, consumers were bound to end up confused.

An attempt to sort out this confusion began in the early 2000s in the United States. Researchers Bruce Nordman and Alan Meier of Lawrence Berkeley National Laboratory pointed out that wasted standby power added up to billions of dollars a year, and drafted a proposal to unify power-related indicators.^[6] That draft was handed off to a standardization working group at the Institute of Electrical and Electronics Engineers (IEEE) in 2002, and was formally published as the IEEE 1621 standard on December 8, 2004.^[7][8] While acknowledging the existing IEC symbols, IEEE 1621 recommended that devices stop relying on the ambiguous “stand-by” symbol and instead use a separate crescent-moon-shaped symbol for low-power states.^[5] Rather than trying to untangle the confusion the stand-by symbol had accumulated, the standard essentially split it off into an entirely different picture.

Ten years later, in January 2014, a new proposal emerged: make these symbols usable as typed, searchable text characters, just like ordinary letters. Written jointly by Terence Eden, Joe Loughry, and the same Bruce Nordman mentioned above, the proposal argued that power symbols — until then embedded only as image files in manufacturers’ manuals — should be registered as searchable character codes.^[8] The proposal was accepted, and four new characters — the vertical line (⏽), the stand-by symbol (⏻), the on/off toggle symbol (⏼), and the crescent-moon-shaped power-saving symbol (⏾) — were added as official codes in Unicode version 9.0, released on June 22, 2016.^[9][10] The circle (⭘), by contrast, had actually already existed as a geometric-shape character in Unicode 5.2 back in 2009; this 2014 proposal simply designated that pre-existing character to also serve, from then on, as the power symbol meaning “fully off.”^[8][9] With this, these symbols could finally be typed directly into emails or documents like ordinary text, without needing to paste in an image file.

A Standard Exists — But Nothing Is Actually Unified

So is the power symbol a genuine, official international standard? On paper, yes. Multiple standards documents — IEC 60417; IEC 60947, which covers industrial switches; and IEEE 1621, which covers user interfaces — all clearly define the shape and meaning of these symbols.^[7][11][13] The Museum of Modern Art (MoMA) has even added the power symbol to its permanent collection as one of the design artifacts representative of the 20th century.^[12] The symbol has become that widely recognized as a piece of visual language.

But a gap remains between the standard documents and the products actually on shelves. More than twenty years after IEEE 1621 was published, no small number of household appliances and electronic devices still use the stand-by symbol (⏻) as a full power on/off button — sometimes even mixing it up with the on/off toggle symbol (⏼).^[5] Some manufacturers use the symbol strictly for its original purpose, indicating a standby state; others just use it loosely to mean “the power button.” Between the bodies that write the standards and the countless manufacturers who actually etch them onto real products, there remains a gap between unenforceable recommendations and long-standing habit. Even IEEE 1621 itself was shifted to “inactive” status in March 2020, for the purely administrative reason that it hadn’t been revised in more than a decade, and it is no longer formally maintained.^[14] Even the standard that sorted out what the symbol was supposed to mean has, in effect, been left unattended.

That gap says something about the limits of standardization as an undertaking. Even when an international body nails down a precise definition in writing, whether individual companies actually honor that definition is ultimately up to them. So at this very moment, the symbol engraved on billions of devices worldwide is carrying, case by case, a slightly different meaning somewhere between what the standard document says and how it’s actually used.

The situation has grown a bit more complicated with recent devices like smartphones and tablets, where physical buttons themselves are disappearing. Manufacturers that display power status through an on-screen software icon each draw the shape and color a little differently. If anything, the symbol’s form is growing more varied now than it was back when everything converged on a single physical button. More than half a century after the international standard was established, the work of standardizing the power symbol is, in a sense, still very much in progress.

For English-speaking readers, this standby confusion already has a name: “vampire power,” also called “phantom load” — the electricity a device keeps drawing even while its screen is dark and its little icon reads as “off.” The phrase became everyday vocabulary across the US, UK, Canada, and Australia as energy bills and consumer advocates made the drain visible.^[15] Washington went further than most: on July 31, 2001, President George W. Bush signed Executive Order 13221, directing federal agencies to buy standby-capable electronics that draw no more than one watt whenever such options were available^[16] — a policy built on the very same Lawrence Berkeley National Laboratory research that shaped IEEE 1621. The gap between what that small icon promises and what the outlet actually delivers, in other words, was never just a design footnote; for a while, it was federal procurement law.

The button we press without a second thought every day is, all at once, the result of translating the numbers 1 and 0 into a picture; a symbol whose meaning expanded outward from the narrow sense of “stand-by” to eventually stand for power in general; and, at the same time, a rare case of something that has an international standard on the books while still being used inconsistently in the real world.