On symbol ( | )

How to read it

The line is IEC 60417-5007. The IEC defines it to indicate connection to the mains, at least for mains switches or their positions, and in all cases where safety is involved. It is usually paired with the circle for off: the draft of IEEE 1621 in Lawrence Berkeley National Laboratory’s 2002 report says the on symbol is best used together with the off symbol, as on a rocker switch. Unicode encodes it as U+23FD, the power on symbol.

Also searched as: line symbol, on symbol.

A 1 and a 0

The line and circle read as the digits 1 and 0. The 2014 proposal to add the power symbols to Unicode typed them as “1” for power on, “binary one”, and “0” for power off, “binary zero”, and showed the pair in the running text of an IBM Personal Computer manual from 1984. Gizmodo’s 2010 history of computer symbols traces the practice to engineers labelling power buttons and switches in the binary system as far back as the Second World War.

Look-alikes

A line inside a circle is a different symbol, the Power on/off symbol symbol, and a line through the gap of a broken circle is the Power symbol.