Blindsight

"Blindsight" was a general term for the natural ability of certain creatures to perceive their surroundings as well as a sighted creature yet without using visual senses. Senses that could contribute to a creature's overall blindsight included enhanced hearing, an acute sense of smell, sensitivity to vibrations, or such specialized senses as echolocation. Because the sense of sight was not involved, a creature with blindsight was not hindered by such spell effects as invisibility or darkness.