How to tell if iphone user is secretly using the iphone

Question

Ipbone usage --  if somebody was sneaking and hiding what they were doing on their phone ie -- instant message thru email vs phone call or text message which will record on phone bill, or using other apps or ? what ever means one could sneak around with-- would it be obvious in the iphones diagnostic and usage dATA ???? by looking at the history would there be a way to dicepher or would it more likely be some jigsaw puzzle ?

Answer 1

Put a passcode on it and don't give the passcode to anyone. Then you will know that no one is using the phone. If the phone in question is not yours, then whether they are using it secretly or openly is probably outside of your control.