Some creatures have Blindsight, the extraordinary ability to use a non-visual sense (or a combination of such senses) to operate effectively without vision. Such sense may include sensitivity to vibrations, acute scent, keen hearing, or echolocation. This ability makes invisibility and concealment (even magical darkness) irrelevant to the creature (though it still can not see ethereal creatures).
This ability operates out to a range specified in the creature description.
Blindsight never allows a creature to distinguish colour or visual contrast. A creature can not read with Blindsight.
Blindsight does not subject a creature to gaze attacks (even though darkvision does).
Blinding attacks do not penalize creatures using Blindsight.
Deafening attacks thwart Blindsight if it relies on hearing (as a bat's echolocation ability does).
Blindsight works underwater but not in a vacuum.
Blindsight negates displacement and blur effects.
Based on the entry in Dungeon Master's Guide 3.5 Page 291.