Power

the binary, made pressable

Unicode: U+23FB power symbol · on U+23FD · off U+2B58 · toggle U+23FC
Meaning: A vertical bar inside a circle: the numeral 1 set within the numeral 0. On, fused with off.
History: Not a design story but a standards story. IEC 60417 registers the family separately — the bar alone for on, the ring alone for off, the two combined for standby, and a bar breaking the ring for a toggle — and the distinctions are precise, widely ignored, and the reason a power button’s behaviour is so often unguessable. IEEE 1621 set out in 2004 to rationalise the mess.
Variants: The four IEC forms are routinely used interchangeably. Manufacturers add their own.
Related: ▶ ⏸ ⏹ the transport set — mechanics that outlived their machines (→ Visual Grammar).
Appears: Every powered device made since the standard, on a keycap, a switch or a screen.
Evolution: Binary notation → standards-body registration → the most-pressed symbol on earth, still ambiguous.

Sources · 3

documented IEC 60417, the registered graphical symbols for use on equipment — 5007 on, 5008 off, 5009 standby, 5010 on/off toggle.
documented IEEE 1621-2004, on the inconsistency of power-state indication in electronic devices.
documented The Unicode Standard: the power symbols encoded at U+23FB–U+23FE in Unicode 9.0 (2016), on a filed proposal — the paper trail of a symbol being admitted to the character set.