The Drive Turnout app runs entirely on your phone - we only track anonymous usage information. No private information is shared back to our servers. The app helps facilitate access to your phone’s address book, your Facebook contacts, and the Pennsylvania state-wide system for ballot tracking, but none of this makes its way to us. We do track the voting status of your contacts, anonymously, as a way of measuring impact.
As far as the privacy of your contacts from you - all of the information presented in this app is already available to you publicly, the app merely serves as a way of helping you keep track of it all in one place.