Power on-off toggle icon: a vertical line inside a closed circle, marking a push-on push-off power button.
U+23FBPOWER SYMBOLU+23FDPOWER ON SYMBOLU+23FABLACK CIRCLE FOR RECORDU+23FEPOWER SLEEP SYMBOLU+23F9BLACK SQUARE FOR STOPU+23FFOBSERVER EYE SYMBOLU+23F8DOUBLE VERTICAL BARU+23F7BLACK MEDIUM DOWN-POINTING TRIANGLEU+23F6BLACK MEDIUM UP-POINTING TRIANGLEU+23F5BLACK MEDIUM RIGHT-POINTING TRIANGLEU+23F4BLACK MEDIUM LEFT-POINTING TRIANGLEU+23F3HOURGLASS WITH FLOWING SAND256 characters in the Miscellaneous Technical Unicode block, from number 253.