How do bats avoid obstacles in their way, when in flight?

Bats fly with speed much lower than the speed of sound. The sounds produced by the flying bats gets reflected back from an obstacle in front of it. By hearing the echo, the bats come to know, even in the dark, the location of the obstacle, so they turn from their path and fly safely without colliding with it. This process of detecting obstacle is called sound ranging.

Bats can produce and detect the sound of very high frequency up to about 100 kHz.