How to Tell if a Switch is On or Off

When the switch is pushed in, the circuit is closed and the power is on. The line symbol means “power on” and the circle symbol means “power off” . The presence of both (I/O) on a push button means the switch toggles the power.

Have you ever found yourself struggling to determine whether a switch is on or off? Mike from Family DIY TV has got you covered. He recently learned a clever hack from a friend that he says makes so much sense, he had to share it with everyone.

Mike starts by acknowledging that many devices have on and off buttons that are not clearly labeled, and he wonders why they don’t just say “on” and “off.” He admits to having a hard time determining whether a switch is on or off, which led his friend’s dad to teach them a helpful trick.

According to Mike, the key to remembering whether a switch is on or off lies in understanding how electricity works. He presents a schematic of a switch and explains that when a switch is on, the current of electricity flows through it, allowing electricity to move from one point to another. In contrast, when a switch is off, there is a break in the system, and the electricity cannot flow through it.

To remember this, Mike’s friend’s dad taught him to think of the “on” switch as having a line that represents the current flowing through it. The “off” switch, on the other hand, has an open circle or “o” that signifies the break in the system.

While some people may find it easy to remember this information, Mike admits to having a hard time with it, which is why this trick has been so helpful to him. He hopes that it will be helpful to others as well, especially those who, like him, struggle to remember which way a switch should be positioned.

So the next time you’re trying to determine whether a switch is on or off, remember that a line indicates that the current is flowing through it, while an open circle or “o” means that the system is broken. With this helpful hack, you’ll never have to guess again.


How do you know when a switch is on or off?
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 I/O or the "I" and "O" characters on top of each other as a single character, as in this photo.
Which is on I or O on a switch?
A common style of a switch is a rocker design, which includes on/off markings. To meet the standard IEC 60417, the symbol for ON is “I” (a straight line) and the symbol for OFF is “O” (a circle).
What is the on off position of a switch?
The "on" position is when the switch is in the up position, and "off" is when it's in the down position. What is the origin of "I" and "O" on the power switches of computers?