The evolution of the On/Off power switch symbol

We all know the symbol with a vertical line in a circle: it identifies the On/Off power switch. It occurred to me that this familiar symbol is evolving in a bizarre fashion.On Off Power Switches

Originally, switches had a lever or slider that could move to either of two physical positions. In those days the switch was marked with the word POWER and its positions with ON and OFF. Then, as switches became smaller and more globalized, the two words were replaced with 1 and 0, as seen even today on many rocker switches.

And then the ubiquity of microprocessors made it more economic to do everything with momentary pushbutton switches; the computer inside could take care of figuring whether you meant ON or OFF. And so, the button now needed an icon that conveys both options; I surmise that is when the familiar “1-inside-a-0″ symbol came into existence (if you know otherwise do share in the comments!) This round icon fit nicely on round buttons, and became ubiquitous.

OnOff power switches

But then we start to see the form shown in the two photos above right: a bastardized version combining the 1-in-a-circle with a 1 in the same symbol. This makes no sense at all - the correct representation would have been 1/0, for On slash Off. Instead we get On slash OnOff. Sloppy thinking…

Such erroneous contractions are often seen in spoken language - as in “IT technology”, which expands to “information technology technology” (there’s even a company by that name, and its slogan, amusingly, is “We make sense of IT“). But now we see the same error invading the more compact space of visual symbols…

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10 Responses to “The evolution of the On/Off power switch symbol”


  1. 1 Dominic Tramontana

    Awesome post, Nathan!

  2. 2 Nick

    i believe the bastardized version of the on off switch actually is also a reset button. So rather than make another symbol for reset the decided to go with on /onoff i think it would make more sense to put on/onoff/off.

  3. 3 Jeff

    I used to think the 1 and the 0 symbols were retarded because nowhere are you told what either one meant. Now that i know that the 1 is a 1 and not just a line ,its not so retarded after all.
    Thank you for setting me straight on these alien symbols.

  4. 4 Robert

    Here is an explanation from IEC and ISO.

    Related to the 0 with a broken ring and a 1 through it. It is soft off.
    >>
    For use on a power switch or button if the off state is soft-off, is variable, is not
    known, or the distinction from hard-off is not important. Also for use with a
    power indicator, or as the icon for the power control panel.
    >>

  5. 5 Arol

    I hope this help us to understand.

    http://en.wikipedia.org/wiki/Power_symbol

  6. 6 Peter-John Taylor

    Excellent, informative and timely post Nathan!

    We’d be very interested to know your thoughts on the matter of poor power switch design and function in general and especially what you think about “Bad design on a UPS” posted by Saaed at
    http://onproductmanagement.wordpress.com/category/business-topics/product-management/

    He writes “Last year, I got my hands on a pretty good UPS for my home computer network. It’s from APC. The model # is the XS1200. It’s a good UPS [which] can take 8 devices plugged into it. Six are managed, two are surge protected only. I’ve got all my critical devices plugged into it including my desktop computer, monitor, cable modem, router, some kind of phone/cable switching device (I get my home phone service through my cable provider), and a couple of other things.

    Now, this is a great device except for one fatal flaw. The round circle on the front is the on/off switch for the UPS. It’s also a very sensitive switch. It doesn’t take more than the soft fingers of a 2 year old child to turn it off. Yes, to turn the whole darn UPS and all 8 devices connected to it off! … I’m sure you can picture what has happened more than once.”

    See APC’s reply at:
    http://www.apc-forums.com/thread.jspa?messageID=8068&tstart=0

  7. 7 john f hubert

    I am a dummy. Is ‘1′ depressed on the rocker switch on or off?

  8. 8 Nathan Zeldes

    ‘1′ depressed on the rocker switch meant “on”, John.

  9. 9 Gilbert Renaut

    There’s a place in England that’s called “Hill Hill Hill” in three different languages, but I can’t remember what it is. Thanks for this, I am setting up a new desktop, and one speaker said don’t plug this in with the power switch on, and I didn’t know which was on.

  1. 1 What does the on/off glyph represent? « Useology

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