The Bat Detector can make the inaudible sounds , which a bat makes in flight , audible.
Sales price € 4,85
Price / kg:

A bat makes sounds that are close to 40,000 Hz, while the human ear of young people but to 20,000Hz gaat.De Bat Detector converts the inaudible sounds of bats to the audible range for humans .

To listen to the sounds have normal headphones with 3.5 mm stereo jack or earbuds as an MP3 / 4 player (not included) The red LED is visible when possible sounds are present , which could come from bats.