Android Action Button

I can't tell when the user hits the main button on their phone the button that i guess i would call the trackball down

I tried this code but it won't work. And i am testing on my droid each build and its annoying because ive tried so many ways to get the input of the user hittign the main button down

I put the code in the Update() loop, the mousedown works on PC but not for android, and Input.inputString is always empty too :(

 if (Input.anyKeyDown)
 {
     var randomness = Random.Range(0,3);
     if (randomness % 2)
     debug_out = "u did it";
     else
     debug_out = "u did it again!";
 }