This sound works really well; I managed to get a bat out of my apartment. Just be persistent. First, I searched the entire apartment, moving furniture, wardrobes, checking corners, curtains, and every nook and cranny, but I couldn't find it. Then I turned off all the lights, sat in one room, turned on these frequencies on studio monitors, and turned up the volume for a few minutes. After a while, it started going crazy around the apartment, flying everywhere, clearly disturbed by the sound. Eventually, I caught it by cornering it with a shoebox and then took it outside with a cloth. The little creature bared its teeth in "self-defense." Although bats navigate through ultrasound (which humans can't hear, in the range of 15 kHz to 90 kHz), they have very poor vision and rely heavily on their hearing to function. Bats produce sounds like squeaks or chirps. Using "echolocation," they can perceive the echoes of sounds they make to navigate and hunt efficiently. Bats can detect frequencies above 100 kHz, and possibly up to 200 kHz, which is beyond human hearing and studio monitors. Therefore, the combination of frequencies up to 20 kHz on this link worked really well.