This means that they sleep during the day and are active at night. Bats are not blind, but they do not usually use their eyes to find food. They have a sophisticated echo location system, similar to sonar. They send a series of sounds through their mouth or nose, then listen for echoes that bounce back when the beeps hit an object. This allows then to tell where an object is and if it is moving.
Different species make different sounds.
There are many misunderstandings about bats - they do not tangle your hair or attack humans. Some species of bats do carry rabies, occasionally. Rabies is a disease that all mammals are susceptible to. Bats benefit people by feeding on harmful insects and some pollinate flowers. This bat benefits the forests by disseminating seeds.