The Simple Bat Detector is a frequency division type device. Frequency division type detectors allow you to hear ultrasonic sound by digitally scaling the frequency down into the human hearing range. For instance, a western pipistrelle bat emits ultrasonic sound in the range of 53 to 91 kHz. If you divide that frequency by 16, the new frequency range is 3.3 to 5.7 kHz, easily within our hearing range. Because the division is done digitally, all amplitude information is lost. Ultrasonic sources processed by the detector convert to sounds like geiger-counter clicks and chirps.