On Off Symbols: What I, O, ⏻ and Power Button Symbols Mean

If you are looking at a switch marked I and O and wondering which one means ON, the answer is simple: I or the vertical line means ON, while O or the circle means OFF. The confusion starts when you see a combined power symbol such as ⏻, a standby symbol, or the letters I/O on electronic equipment.

I’m going to break these on off symbols down in a practical way so you can recognize them on switches, computers, TVs, monitors, power strips, appliances, and other equipment. You’ll also see why the symbols are used, how ON differs from standby, why I/O does not always mean ON/OFF, and why an equipment button showing “off” should not automatically be treated as proof that every internal part is electrically safe.

The key idea is this: read the symbol and the context together. A simple rocker switch may give you a straightforward ON/OFF choice, while a modern electronic device may have several power states.

Quick Answer: Which On Off Symbol Means ON and OFF?

For the most common power markings, remember:

IEC 60417 identifies 5007 as “ON” (power) and 5008 as “OFF” (power). It also distinguishes 5009 for Stand-by and 5010 for ON/OFF push-push controls.

The easiest rule to remember

I = ON
O = OFF

Think of the vertical line as the ON position and the circle as the OFF position.

The association with 1 = ON and 0 = OFF is a useful memory trick, but it is better not to treat that as the formal reason for the standardized symbols. Their meanings come from the equipment-symbol system itself.

What Do the I and O Symbols Mean on a Switch?

The familiar I/O markings are graphical symbols used to communicate equipment functions. They are not simply ordinary English letters printed on a switch.

ISO explains that graphical symbols are used on equipment to communicate information about how equipment should be operated, while the ISO 7000 and IEC 60417 collections contain standardized equipment symbols.

That is why the same basic idea can appear on equipment made for people who speak different languages.

I or the Vertical Line Means ON

The I-like vertical line represents the ON power state in the common IEC power-symbol system.

IEC 60417 reference 5007 is titled “ON” (power) and is used to indicate connection to the mains, including mains switches or their positions in relevant safety situations.

So, if a rocker switch is marked:

I | O

the I side is the ON side.

For example, you might find this marking on:

• A desktop computer power supply
• A power strip
• An appliance
• An electronic device
• Industrial equipment
• A mains switch

O or the Circle Means OFF

The O or circle represents the OFF power state in the same standardized system.

IEC 60417 reference 5008 is titled “OFF” (power) and indicates disconnection from the mains for the applicable switch or position.

So if you see:

I | O

the O side is OFF.

This is one of the most useful pieces of information to remember when you are dealing with a simple rocker switch.

Why Do I and O Look Like 1 and 0?

There is an easy visual memory trick:

I → 1 → ON

O → 0 → OFF

That can help you remember the symbols when you are standing in front of an unfamiliar switch.

However, don’t describe the formal standard as simply “the symbols are binary numbers.” The standardized meanings come from the graphical-symbol system. The 1/0 association is best treated as a convenient way for users to remember them.

Which Side of a Rocker Switch Is ON?

On a rocker switch marked I and O, the side marked I is the ON position and the side marked O is the OFF position.

The physical direction is not universal.

For example, one switch might be mounted horizontally:

I — O

Another might be installed vertically:

I
O

The symbols still tell you what the positions mean.

Read the Symbol, Not the Direction

A common mistake is assuming:

“The left side must be ON.”

or:

“The top side is always ON.”

Neither is a reliable rule.

The better rule is:

Find the I or line marking. That is the ON position. Find the O or circle marking. That is the OFF position.

This becomes especially useful when equipment is mounted upside down, sideways, behind a desk, or in a cramped space.

What Does the ⏻ Power Symbol Mean?

The familiar power-button symbol is common on modern electronics.

You may find it on:

• Computers
• Monitors
• Televisions
• Speakers
• Printers
• Chargers
• Appliances
• Electronic control panels

It is often drawn as a circle with a vertical line entering or crossing it.

The important point is that you should not assume every power-looking symbol means exactly the same electrical state.

IEC 60417 has separate symbols for ON, OFF, standby, and ON/OFF controls. That distinction matters because modern equipment can have several different power conditions.

Why the Power Button Can Be Confusing

A modern electronic device may not use a simple mechanical switch.

When you press a power button, the device could:

• Enter normal operation
• Enter standby
• Enter a low-power state
• Shut down its main functions
• Remain connected to the mains while consuming a small amount of power

The exact behavior depends on the equipment.

That is why the symbol tells you the intended control function, but it does not describe every detail of the circuit inside the device.

What Is the Difference Between ON, OFF, Standby and Sleep?

This is where many people get confused.

A device can have more than two meaningful states.

These terms are related, but they are not automatically interchangeable.

IEC 62301:2026 specifically addresses the measurement of electrical power in standby and other non-active modes, including off mode, which reflects the fact that different inactive states can have different technical characteristics.

OFF Does Not Always Mean “No Electricity Anywhere”

This is one of the most important practical distinctions.

For normal use, saying:

“I turned the TV off.”

is perfectly natural.

But from a technical or servicing perspective, another question matters:

Is the equipment completely disconnected from its electrical source?

A device may still have standby circuitry, a battery, stored electrical energy, or another power path depending on its design.

So:

OFF ≠ automatically safe to open.

For internal electrical work, use the manufacturer’s instructions and appropriate isolation procedures rather than relying only on a button or symbol.

Standby Is a Different State

IEC 60417 reference 5009 is the Stand-by symbol. It identifies a switch or position that brings part of equipment into the standby condition.

A standby device may remain ready to:

• Receive a remote-control signal
• Respond to a control input
• Maintain certain electronic functions
• Preserve settings or memory
• Perform limited background functions

The exact behavior depends on the device.

What Does the ON/OFF Push-Push Symbol Mean?

Not every power switch has separate physical I and O positions.

IEC 60417 reference 5010 identifies an ON/OFF push-push control. Its ON and OFF positions are stable positions.

This is different from a button that simply springs back after you press it.

With a push-push mechanism:

Press once → ON

Press again → OFF

The button may look almost the same after each press, but the internal switch state changes.

Why This Matters

If you are trying to determine whether a device is switched on, don’t always judge by how far a button sticks out.

Look at:

• The symbol
• The indicator light
• The display
• The equipment’s behavior
• The manufacturer’s instructions

The physical appearance of the button is not necessarily a reliable indication of its electrical state.

What Does the I/O Label Mean?

This is an important point that many simple articles miss.

I/O does not always mean ON/OFF.

In some switch contexts, I and O are used for the ON and OFF positions.

But in computers, electronics, and technical documentation, I/O commonly means Input/Output.

For example:

I/O ports

usually refers to input/output connections or functions, not an ON/OFF switch.

Technical symbol collections also contain separate symbols for input, output, and input/output functions.

How to Tell Which Meaning Applies

Use the surrounding context.

If you see:

I — O

on a physical rocker switch, it is likely an ON/OFF marking.

If you see:

I/O ports

on a computer or motherboard, it is referring to Input/Output.

If you see:

I/O panel

in a computer manual, it usually refers to the panel containing connections such as USB, audio, display, networking, and other interfaces.

This distinction prevents a surprisingly common misunderstanding.

Why Are On Off Symbols Used Instead of Words?

The main advantage is clear graphical communication.

Equipment can be sold internationally. A graphical symbol can communicate a function without requiring the manufacturer to print the word “ON” in every language.

ISO describes ISO 7000 as a collection of graphical symbols placed on equipment to help users understand operation. The ISO and IEC collections cover equipment ranging from consumer products to industrial machinery.

Symbols Make Equipment Easier to Understand

Imagine a product sold in many countries.

Instead of printing:

ON / AUS / MARCHE / ENCENDIDO / LIGADO

a manufacturer can use an established graphical symbol.

That makes the interface more compact and easier to recognize.

Symbols Are Especially Useful on Small Controls

A word may take up valuable space on:

• Small switches
• Remote controls
• Computer buttons
• Appliance panels
• Portable electronics
• Industrial controls

A simple symbol can communicate the function without requiring a large label.

On Off Symbols on Common Devices

Understanding the basic symbols becomes much easier when you see how they appear in real situations.

Desktop Computers

A desktop computer can have two different types of power controls.

The power supply at the back may have a physical rocker switch marked:

I / O

In that case:

I = ON

O = OFF

The front power button may use a power symbol and interact with the computer’s operating system.

That means the rear power switch and front power button should not automatically be treated as identical controls.

Computer Monitors

A monitor may use a power button or touch-sensitive control marked with a power symbol.

When you turn the monitor “off,” its display stops operating, but the exact electrical state depends on the monitor’s design.

Some equipment can remain connected to the mains while operating in a low-power state.

Televisions

A television is another good example.

Pressing the power button may make the screen go dark while the television remains in standby.

This allows the TV to respond quickly to a remote control or another supported command.

So:

Black screen does not necessarily mean complete electrical disconnection.

Power Strips and Extension Boards

Many power strips have a simple rocker switch.

You may see:

I | O

Press the I side and the controlled output is switched ON.

Press the O side and it is switched OFF.

This is one of the clearest real-world examples of the I/O power convention.

Household Appliances

Appliances can use different kinds of power controls.

You might find:

• I/O rocker switches
• Push buttons
• Power icons
• Standby controls
• Rotary controls
• Manufacturer-specific markings

The symbol should always be interpreted in the context of the appliance.

UPS Systems

A UPS is a special case because it may contain:

• A mains input
• Rechargeable batteries
• An inverter
• Output circuits
• Charging electronics
• Control electronics

Switching a UPS off does not mean its battery has suddenly stopped storing energy.

For servicing, follow the manufacturer’s procedures rather than treating the OFF marking as proof that stored energy is absent.

Why a Device Can Be Off but Still Use Some Power

This is one of the most useful concepts to understand if you are researching on off symbols.

Modern electronics can have circuits that remain active in non-operating states.

For example, a device may need a small amount of power to:

• Detect a remote-control command
• Maintain a network connection
• Keep a clock running
• Preserve settings
• Monitor a button
• Manage charging
• Respond to a wake signal

IEC 62301:2026 recognizes standby and other non-active modes as measurable electrical states. It also covers off mode and other conditions in which equipment is not performing its main function.

This is why the simple everyday phrase “off” and the technical question “is the equipment drawing any power?” are not always identical.

How to Identify an Unclear On Off Symbol

Sometimes the marking is faded, scratched, dirty, or difficult to see.

Use this practical process.

First, Look for the Basic I and O

If you can identify:

I / |

that is the ON marking.

If you can identify:

O / ○

that is the OFF marking.

Next, Check Whether It Is a Power Button or Rocker Switch

A rocker switch with two physical positions is different from a momentary push button.

Ask:

• Does the switch stay in one of two positions?
• Does the button spring back?
• Is there a power indicator?
• Does the device have standby behavior?

These clues help you understand the control.

Check the Equipment Label or Manual

If the symbol is unusual, the manufacturer’s manual is the best source for the specific device.

This is particularly important when:

• The equipment has multiple power sources
• The device contains a battery
• The device is industrial
• The switch controls only part of the equipment
• The device has a standby mode

Do Not Guess When Electrical Safety Is Involved

If the question is simply:

“Which side turns my power strip on?”

the I/O rule is usually enough.

If the question is:

“Can I open this device now that I pressed OFF?”

that’s a different situation.

Do not use the symbol alone as a safety test.

Common Mistakes About On Off Symbols

Mistake: Thinking O Means ON

The circle is the common OFF power symbol.

Remember:

O = OFF

Mistake: Thinking I Is Just the Letter I

It may look like a letter, but it functions as a graphical equipment symbol in the standardized system.

Mistake: Assuming the Left Side Is Always ON

The orientation of a switch can change.

The marking matters more than whether the switch is on the left, right, top, or bottom.

Mistake: Assuming Every ⏻ Symbol Means Complete Disconnection

Power-control symbols need to be interpreted in context.

Modern devices may use power buttons to control operating states rather than provide the same physical isolation as a dedicated mains switch.

Mistake: Thinking a Dark Screen Means Zero Power

A display can be dark while the equipment remains connected to power or in a low-power state.

Mistake: Assuming I/O Always Means ON/OFF

In computing and electronics, I/O often means Input/Output.

Always check the context.

Mistake: Using a Power Symbol as a Safety Test

A button labeled OFF is not a replacement for proper electrical isolation procedures when equipment is being serviced.

ON vs OFF vs Standby: A Practical Comparison

If you are unsure which power state you are looking at, this comparison can help.

The table is useful because it separates what the user sees from what the equipment may technically be doing.

A Simple Decision Guide for Reading Power Symbols

When you encounter an unfamiliar symbol, work through these questions.

Do You See I or a Vertical Line?

Yes → It represents ON.

This is the easiest case.

Do You See O or a Circle?

Yes → It represents OFF.

Again, this is the basic power-symbol convention.

Do You See a Combined Power Symbol?

Check the exact symbol and equipment documentation.

It may represent a power control, ON/OFF function, or another defined operating state.

Does the Device Mention Standby?

Treat standby as a separate state.

A standby device may remain connected and may continue using some power.

Does the Label Say I/O?

Check the context.

On a rocker switch, it can indicate ON/OFF.

On a computer or electronic interface, it can mean Input/Output.

Are You About to Open or Repair the Equipment?

Stop relying on the symbol alone.

Follow the manufacturer’s safety instructions and appropriate electrical isolation procedures.

Why Standardized Symbols Matter for International Equipment

A major strength of graphical symbols is that they reduce dependence on written language.

ISO 7000 describes registered graphical symbols for use on equipment and gives each symbol a reference number, meaning, graphical representation, and other relevant information.

The ISO/IEC symbol collection is used across many categories of equipment, including consumer and industrial products.

This matters because an appliance or electronic device may be manufactured in one country, sold in another, and used by someone who speaks an entirely different language.

A recognizable symbol can make the control easier to understand without translating the entire interface.

How the Same Basic Idea Appears in Different Forms

You may see several visual versions of the same basic power concept.

Separate I and O

This is common on physical switches:

I | O

The two symbols identify two positions.

A Power Button Symbol

A combined circle-and-line design is common on electronic devices.

The exact function depends on the applicable symbol and the equipment’s design.

Standby Symbol

A standby marking identifies a standby-related state rather than simply being another way to write “OFF.” IEC 60417 treats standby as a separate symbol from the basic ON and OFF power symbols.

Part-of-Equipment Symbols

IEC also includes separate symbols for the ON and OFF condition of a part of equipment when the standard whole-equipment symbols are not suitable. For example, references 5264 and 5265 identify ON and OFF for a part of equipment.

This is an important technical detail because a switch may control only one section of a larger machine rather than the entire system.

Why “ON” Does Not Always Mean the Entire Device Is Running

A control can be associated with one part of a system.

For example, a machine may have:

• A main power switch
• A display switch
• A motor control
• A lighting control
• A standby control
• An emergency stop

Therefore, the ON marking should be interpreted according to what that particular control operates.

IEC’s symbol collection includes specific symbols for ON and OFF conditions of parts of equipment, which reinforces this distinction.

This is why experienced users don’t assume that every ON marking means every function of the entire machine is active.

On Off Symbols and Electrical Safety

For ordinary everyday use, identifying the symbols is simple.

The important safety distinction appears when someone moves from using equipment to servicing equipment.

If you are repairing a device, do not assume:

“The button says OFF, so there is definitely no hazardous energy inside.”

Electrical equipment can have:

• Stored energy
• Batteries
• Capacitors
• Multiple power sources
• Standby circuits
• External power connections

The appropriate isolation procedure depends on the equipment.

For ordinary users, the safest approach is to follow the manufacturer’s instructions and avoid opening equipment that requires electrical servicing unless you are qualified to do so.

Frequently Asked Questions About On Off Symbols

Which symbol means ON, I or O?

I or the vertical-line symbol means ON. O or the circle symbol means OFF for the standard power markings discussed here. IEC 60417 identifies 5007 as ON (power) and 5008 as OFF (power).

Does the line mean ON?

Yes. The vertical-line form represents the ON power symbol in the relevant IEC equipment-symbol system.

Does the circle mean OFF?

Yes. The circle represents the OFF power symbol in the relevant IEC system.

What does ⏻ mean?

It is a commonly recognized power-control symbol. The exact technical function depends on the specific symbol and equipment. IEC distinguishes several power-related functions, including ON, OFF, standby, and ON/OFF controls.

What does the standby symbol mean?

It identifies a standby-related state. Standby is not simply another name for every possible form of OFF. IEC 60417 identifies 5009 as Stand-by.

Is I/O always an ON/OFF symbol?

No. On a physical power switch, I and O can represent ON and OFF. In computing and electronics, I/O commonly means Input/Output.

Why does my TV look off but still have a light?

The TV may be in standby or another low-power state. The exact behavior depends on the model.

Does switching something OFF mean it uses no electricity?

Not necessarily for every device. Some equipment can have standby or other non-active modes that still consume electrical power. IEC 62301:2026 specifically addresses measurement of standby and other non-active modes, including off mode.

Which side of an I/O rocker switch is ON?

The side marked I or the vertical line is ON. The side marked O or the circle is OFF.

Why don’t manufacturers simply write ON and OFF?

Graphical symbols provide a compact, language-independent way to communicate equipment functions. ISO 7000 and IEC 60417 provide standardized graphical-symbol collections for equipment.

Are these symbols internationally standardized?

Many equipment symbols are standardized through systems such as ISO 7000 and IEC 60417. The standards provide registered graphical symbols and their meanings for equipment use.

Can I safely open equipment after switching it OFF?

Not necessarily. A power symbol tells you about the intended control state; it is not, by itself, proof that stored energy or every electrical source has been eliminated. Follow the manufacturer’s service instructions and appropriate electrical safety procedures.

What is the easiest way to remember I and O?

Use this simple rule:

I = ON

O = OFF

Then remember the second rule:

OFF, standby, and completely disconnected are not necessarily the same thing.

Key Takeaways

If you only need the essential information, remember these points:

• I / vertical line = ON
• O / circle = OFF
• ⏻ = power control; interpret the exact symbol and device context
• Standby is a separate power state
• I/O can mean ON/OFF or Input/Output depending on context
• A dark screen does not necessarily prove that a device is completely disconnected from electricity.
• The physical direction of a rocker switch is not universal; read the marking.
• Standardized equipment symbols exist so controls can be understood more consistently across languages and products.
• For electrical servicing, do not use an ON/OFF symbol as your only safety test.

The most useful mental shortcut is simple:

Line = ON. Circle = OFF.

Once you understand that basic rule, the next step is recognizing that modern equipment can have several states between “fully running” and “physically disconnected.” That is why standby, sleep, power buttons, and I/O labels sometimes require a little more context.

Conclusion

On off symbols look simple, but they carry more information than many people realize. The basic rule is straightforward: I or the vertical line represents ON, while O or the circle represents OFF in the standard power-symbol context.

The confusion usually begins when a simple I/O rocker switch is compared with the power button on a modern computer, television, monitor, or appliance. Those devices may support standby and other low-power states, so pressing a power button does not necessarily mean the same thing as physically disconnecting the equipment from its power source.

It is also important not to confuse I/O as a switch marking with I/O as Input/Output in computing and electronics. Context tells you which meaning applies.

The broader reason these symbols exist is practical: standardized graphical symbols make equipment controls easier to understand across languages and product categories. ISO 7000 and IEC 60417 provide systems for graphical symbols used on equipment, while IEC 62301 recognizes that standby and other non-active power states can have distinct electrical characteristics.

So the next time you see a switch marked I and O, you do not need to guess:

I = ON.
O = OFF.

And if you see a more complicated power symbol, don’t stop at its appearance. Check what the exact symbol represents and how that particular equipment is designed to operate.

Lucas Thompson

I’m Lucas Thompson, a writer with a strong interest in vocabulary and everyday communication. I enjoy researching words that people encounter in conversations, online communities, and social media. At Meanera, I explain their meanings, context, and common usage in straightforward English so readers can find the answer they need quickly.

Books:

• The Everyday Wordbook
• English Beyond the Dictionary