Canon PowerShot S400 Digital Elph User Manual page 19

The i ndicators light orblink w hen t he ON/OFF Button orshutter
button ispressed.
Upper Indicator
Green: Ready to shoot
Blinking Green: Recording to CF card / Reading CF card/Erasing
from CF card/Transmitting data (during a
computer connection)
Orange: Ready to shoot (flash on)
Blinking Orange: Ready to shoot (camera shake warning)
Lower Indicator
Yellow: Macro mode/Infinity mode/Focus lock (Method 2,
p. 64)
Blinking Yellow: Focusing difficulty (1 beep sounds).
Although you can press the shutter button, you are
recommended to use the focus lock (p. 64).