Your phone needs to be in your front pocket during your round (Android users should keep it in your front leading pocket i.e., left front pocket if you are a righty). Arccos employs the GPS capabilities of your iPhone to know where you are and where you're hitting your shots from. Our 2nd generation 360 sensors also use the microphone in the phone for shot detection. Without the phone in your front pocket, the Arccos app will not work.
For players who do not like to play with a phone in their pocket, our best suggestion is to use a belt clip.