Originally posted by K(s)evin It's just letting you know that your settings (shutter, aperture & iso) are outside of what the metering system says will give you an effective exposure.
Close...
Originally posted by splash_fr You're in manual mode and the cam is telling you that you're underexposing.
Note the EV scale. In M-mode the camera is usually quite happy to let you set underexposure, no blinkies, as long as the ambient light is within the meter range. In the above photo in the original post, the meter reading (what shows in the EV scale) says -3 stops underexposed, but the camera is warning that the light to the meter is less than -3 EV
100 (below meter sensitivity, meaning that the underexposure is likely more than the -3 stops shown on the EV scale).
The more common source of red blinkies on the exposure line in live view is with automated exposure where the metering indicates a setting outside what may be set on the camera (e.g. Tv mode where f/2.0 would be required, but the mounted lens is f/2.8 maximum aperture). In both cases, the shutter button will still work, but what you get is not the meter's fault, hence the red blinkies. The blinkies just indicate an "out of bounds" condition.
FWIW...none of this is in the manual and actually required some walking into dark rooms this morning with my K-3. My post above regarding HDR and/or bracketing was wrong. The camera is quite willing to attempt a bracket series even when that series means going out-of-bounds. It does not even blink!
Steve