A friend of mine has wanted to make a predator calling app for quite some time, and we finally agreed to work on it together. He recorded all the sounds using various methods he uses while hunting and provided the images. I used Unity3D to put together an App with a scrolling button view and then added some logic to allow the sounds to loop when needed.
For both Android & iOS I was able to hook into the device volume controls directly, so the on-screen slider actually changes the device volume. I was also able to make use of the iOS method to control bluetooth audio routing without writing custom code. On Android, the user must set the routing using the system controls.
For both devices I had to write a custom audio playback system to overcome the limitations Unity exhibits when background audio is interrupted, or when the device sleeps. I created a custom NativeAudio class and then hooked into different native code written in ObjectiveC and Java that provided a neutral interface to the device specific systems.
Finally, the App is free to download and has an in-app-purchase to unlock all the sounds. Without the upgrade only the first 15s of each sound can be played, and looping is disabled.
You can check it out here: ultimatepredatorcalls.com.