"No data leaves the device" is such a vague policy that it means nothing. At a minimum, your app displays some UI containing its data. Bravo, information from

"No data leaves the device" is such a vague policy that it means nothing. At a minimum, your app displays some UI containing its data. Bravo, information from the app now leaves the device through the photons emitted by the screen. Same for speakers. Now consider the clipboard. The user copies some text from your app and pastes it into an online forum. Bravo, information from the app now leaves the device through the clipboard.