When you are using electronic gadgets, did it ever occur to you how the power button symbol came about? It is safe to say we are accustomed to the familiar ‘broken circle and vertical stroke’ symbol and we’d forgive ourselves for taking it for granted. However, like most things in life, this humble symbol has a short but no less interesting story. If you look closely, the “broken circle and vertical stroke” symbol is actually a combination of ‘0’ and ‘1’, the binary number system that represents off and on states. Prior to using 0 and 1, which was sometime around WWII, power control switches are labelled ‘On’ and ‘Off’, but as time goes by, engineers began to devise a simpler labelling that would transcend language barriers and hence, the universally recognized 0 and 1 was chosen to represent ‘on’ and ‘off’, which was used on toggle switches (see below).
Along the way, as technology advances and single on/off button becomes ubiquitously used, a symbol that superimposed “0” and “1” was created to indicate the button is both an ‘on’ and ‘off’ button. And then sometime in 1973, the International Electrotechnical Commission or I.E.C. officially gave the stamp of approval for this symbol as a universal power button. But that’s not the end of this short but interesting story. This power button symbol is not quite the power, power button as you know it to be. It is in fact, is more of a standby symbol, meaning, the deactivation merely puts the device to sleep mode or to low power state, and the power supply is not entirely cut off. In other words, electricity is still all over the device, albeit at much lower power level.
This is also why certain electronic equipment, especially those with high power supply, has this ‘standby button’ and yet another toggle switch to completely disconnect the device from the power. This also explains why when a so-called off device can be turned on with a remote cos’ in reality, if it is “turned off” there would be no power supply to allow for the action of turning on to take place. So, there you have it, the story of the origin of the Power button symbol.
Additional info via Wikipedia