Mindsight( Lords of Madness, p. 126)
A creature that has this feat possesses innate telepathic ability that allows it to precisely pinpoint other thinking beings within range of its telepathy. The creature perceives where the others are and how powerful their intellects are.
Telepathy special quality,
A creature that has this feat can detect and pinpoint beings that are not mindless (anything with an Intelligence score of 1 or higher) within range of its telepathy. This works much like blindsense--the creature knows what square each thinking being is in, but it does not see the being, and the being still has total concealment unless the creature can see it by some other means. The creature also perceives several observable characteristics about each being detected with mindsight, including the being's type and Intelligence score. The creature need not take any additional or special actions to gain this information; it is as obvious to mindsight as the being's race and clothing would be to eyesight.
Telepathy offers no special ability to sense other minds. The creature has to know that a being is there to communicate with it telepathically.