Power button on laptop

The power button is a round or square button that powers an electronic device on and off. Nearly all electronic devices have power buttons or power switches.

Typically, the device powers on when the button is pressed and powers off when it's pressed again.

A hard power button is mechanicalyou can feel a click when pressed and usually see a difference in depth when the switch is on versus when it's not. A soft power button, which is much more common, is electrical and appears the same when the device is on and off.

Some older devices instead have a power switch that accomplishes the same thing as a hard power button. A flip of the switch in one direction turns the device on, and a flip in the other turns the device off.

On/Off Power Button Symbols (I & O)

Power buttons and switches are usually labeled with "I" and "O" symbols.

The "I" represents power on and the "O" represents power off. This designation will sometimes be seen as I/O or as the "I" and "O" characters on top of each other as a single character, as in the following photo.

Power Buttons on Computers

Power buttons are found on all kinds of computers, like desktops, tablets, netbooks, laptops, and more. On mobile devices, these are usually on the side or top of the device, or sometimes next to the keyboard, if there is one.

In a typical desktop computer setup, power buttons and switches appear on the front and sometimes back of the monitor and on the front and back of the case. The power switch on the back of the case is actually for the power supply installed in the computer.

When to Use the Power Button on a Computer

The ideal time to shut down a computer is only after all the software programs are closed and your work is saved. However, even then, using the shutdown process in the operating system is a better idea.

A common reason you'd want to use the power button to turn off a computer is if it's no longer responding to your mouse or keyboard commands. In this case, forcing the computer to power off using the physical power button is probably your best option.

Please know, however, that forcing your computer to shut down means all the open software and files will also be ended without any notice. Not only will you lose what you're working on, but you can actually cause some files to become corrupt. Depending on the files that are damaged, your computer may fail to start back up.

Pressing the Power Button Once

It might seem logical to press the power once to force a computer to shut down, but that often doesn't work, especially on computers made in this century (i.e., most of them!).

One of the advantages of soft power buttons, which was talked about in the introduction above, is that, since they're electrical and communicate directly with the computer, they can be configured to do different things.

Believe it or not, most computers are set up to sleep or hibernate when the power button is pressed, at least if the computer is working properly.

If you really need to force your computer to shut down, and a single press isn't doing it (pretty likely), then you'll have to try something else.

How to Force a Computer to Turn Off

If you have no choice but to force the computer off, you can usually hold down the power button until the computer no longer shows signs of powerthe screen will go black, all the lights should go off, and the computer will no longer make any noises.

Once the computer is off, you can press the same power button once to turn it back on. This type of restart is called a hard reboot or hard reset.

How to Turn Off a Device Without Using the Power Button

If at all possible, avoid just killing the power to your computer, or to any device! Ending running processes on your PC, smartphone, or another device without a "heads up" to the operating system is never a good idea, for reasons you've already read about.

Another reason you might need to turn off or restart a computer without using the power button is if the button is broken and won't work like it's supposed to. This can happen on phones and computers alike.

See How Do I Restart My Computer? for instructions on properly turning off your Windows computer. Turning off other devices like tablets and smartphones usually involve holding down the power button and following the on-screen prompts.

More Information on Powering Off Devices

A strictly software-based method to turn off a device is usually available, but not always. The shutdown of some devices are triggered by the power button but even then are finished up by the operating system it's running.

The most notable example is the smartphone. Most require that you hold down the power button until the software prompts you to confirm that you wish to turn it off. Of course, some devices don't run an operating system in the typical sense and can be safely shut down by simply pressing the power button oncelike a computer monitor.

How to Change What the Power Button Does

Windows includes a built-in option to change what happens when the power button is pressed.

1. Open Control Panel.

2. Go into theHardware and Soundsection. It's calledPrinters and Other HardwareinWindows XP.

   Don't see it? If you're viewing Control Panel where you see all the icons and not categories, you can skip down to Step 3.

3. ChoosePower Options.

   In Windows XP,this option is off to the left side of the screen in theSee Alsosection. Skip down to Step 5.

4. From the left, pick Choose what the power buttons doorChoose what the power button does, depending on the Windows version.

5. Choose an option from the menu next toWhen I press the power button:. It can beDo nothing, Sleep, Hibernate,orShut down. In some setups, you might also see Turn off the display.

   Windows XP Only:Go into theAdvancedtab of thePower OptionsPropertieswindow and select an option from theWhen I press the power button on my computer:menu. In addition toDo nothingandShut down, you have the optionsAsk me what to doandStand by.

   Depending on whether your computer is running on a battery, like if you're using a laptop, there will be two options here; one for when you're using battery and the other for when the computer is plugged in. You can have the power button do something different for either scenario. If you can't change these settings, you might first have to select the link calledChange settings that are currently unavailable. If the hibernate option isn't available, run thepowercfg /hibernate oncommandfrom anelevated Command Prompt, close down every open Control Panel window, and then start over at Step 1.

6. Be sure to select Save changesorOKwhen you're done making changes to the power button's function.

You can now close down any Control Panel or Power Options windows. When you press the power button from now on, it will do whatever you chose it to do in Step 5.

Other operating systems might also support changing what happens when the power button is used, but they probably only support non-shutdown options like opening apps and adjusting the volume.

Buttons Remapper is one example of a tool for Android devices that should be able to remap the power button to make it do something other than power down the device. It can open the last app you were in, adjust the volume, open the flashlight, start the camera, begin a web search, and lots more. ButtonRemapper is very similar.

Frequently Asked Questions

• How did the symbols "I" and "O" come to represent on and off, respectively? The symbols are based on the binary number system, where "1" represents "on," and "0" represents "off."
• How do I read various on and off symbols? An easy way to remember: 0 = false, meaning no power or off; and 1 = true, or on. (In the case of I/O, the 'I' represents 1.) So, if a switch is turned to I, it's in the On position. If it's turned to O, it's in the Off position.