Echolocation
Bats have the same basic auditory system as all mammals only theirs has evolved to be highly sensitive so that sound can be utilized as a method of seeing. Bats utilize ultrasonic sound (greater than 20 kHz), which most mammals cannot hear, during echolocation.
A large ossified larynx allows the bat to build up a lot of tension on the vocal cords. The bat can then emit sound waves, through either its nose or mouth, which can reach up to 150 kHz. These high frequency sound waves are far closer together than low frequency sound waves. This gives the bat more information about its surroundings when the information is processed by the brain. These waves can be emitted 100 times per second as the bat stalks its prey.
Interestingly, in the Microchiroptera family, successful foraging, particularly in clutter, is sometimes hindered by echolocation. Some species use calls which are clutter-resistant, whereas others forsake echolocation while hunting. In some cases, foraging success may be more limited by echolocation than by flight performance. In any case, it has been observed that in captivity, Greater False Vampire Bats can successfully detect and catch mice and frogs in complete darkness without echolocating.
Read more about this topic: Greater False Vampire Bat