A free program for Android, by Sergio Gudkov.

If you want to detect ultrasound acoustic signals above the user-defined frequency (above 18 KHz by default), you can download the Ultrasound Detector app for free.

The app can be used to detect ultrasonic sounds and vibrations. You can utilise it to determine the presence of Ultrasonic Cross-Device Tracking technology in some public places. Additionally, this app will come in handy when you are testing if electronic pest and insect repellent devices are working properly.

Furthermore, you may also use this app in locating the leaks in refrigeration or air conditioning systems.