Bats use echolocation by emitting sound waves; when those sound waves hit a nearby object, it produces an echo that is then bounced back to the bat. The bat then deciphers the echo as the existence of an object in the direction from which the echo came.
Bats utilize echolocation as a means of navigating in the dark and locating their prey. Some bats emit sounds from their mouths, while others use their noses to echolocate. This allows them to pinpoint their prey even in the darkest of caves.
When a bat listens to the sound wave returned to it, its brain decodes the sound and determines exactly how far away the object is by considering the time it took for the sound to return. The longer it takes for the sound wave to return to the bat, the farther away the object is. Using echolocation, the bat can also determine how big the object is, whether or not it is moving, and in what direction.
A bat can tell whether an object is to the left or right side of it by comparing the time the sound takes to reach its left ear with the time it takes to reach its right. If the sound reaches the bat's left ear before it reaches the right ear, then the bat can conclude that the object is on its left side.
In most cases, the sound a bat produces when using echolocation is extremely high pitched and beyond the hearing range of a human.