How can bats move about freely even in a total darkness?

A bat can hear ultrasound at frequencies upto 120 kHz. During their flight, bats emit a series of high frequency ultrasound pulses. It is able to detect the presence and location of any nearby object from the reflected sounds for which the bat has a sophisticated built-in receiver. Therefore the bat is able to sense the time it takes for the ultrasound pulses to return after being reflected by an object. Thus, bats can move freely even in a total darkness.