The Anabat detector is a device that allows a researcher to hear and see bat calls. The bats we study are nocturnal insectivores. This means that the bats feed on insects at night. Optical vision is not an effective tool to use for finding bugs in the dark.
Here is a picture of Michael O'Farrell and Bruce Miller using an Anabat detector in Belize. The picture is from an article titled "Chasing the Ghost Bat" which appeared the June 1999 issue of Scientific American. They are holding the microphone and speaker assembly.
This picture shows a live graph of several bat calls.
This graph of echo location calls from a little brown bat was recorded at the Neda Mine in the fall of 1999. At the beginning of the graph you will see a burst of activity between 40 and 60 kHz (Kilo Hertz or thousands of cycles per second). Later you will see brief echolocation calls. The bursts are normally seen when the bat is hunting and detected a prey insect. When the bat locates an insect it increases the amount of echo location calls to home in on the insect to eat it. Because it takes a great deal of energy to emit and process the echolocation calls the bat only uses them when it is locating objects or food.
This picture shows two feeding bursts from a bat.
The bats are able to detect very small objects, on the order of the diameter of a human hair. Why do you think that a bat will sometimes fly into a persons hair if they are able to see something as small as a single hair? It may be that the bats are attracted to the insects that are attracted to you! When chasing a tasty bug the bat may become so excited that he will run right into you. While I always wear a hat when working at the mine entries, I have been bumped many times without any ill effect. In fact the bats seem to largely ignore humans that they encounter in their habitat.