how to detect if my game is running on iphone or in Unity?

When running on the iPhone the user input will be via tilt of the device. If running on Unity the user input will be the arrow keys.

I have the code to handle user input. But how do I tell in my c# script if the app is running on the iphone or in Unity?

I want something I can put in a if-statement so I can read the keyboard or read the accelerator.