Data on the phones was recorded by a user-level agent developed as part of the study. Data was recorded primarily via periodic polling (current wireless consumption, application consumption, wireleless state) with triggers are used as appropriate for data that was of increased time sensitivity (ex. screen on, wireless roam). At periodic intervals, data was securely sent to the central study servers (see 6 for more details). The initial instantiation of the agent was a custom APK (Android application package file) while a Play STore app was distributed in late fall / early spring of 2013 / 2014. For the purposes of this paper, there are several key attributes that should be noted :