The above is correct; just want to add: We have added the "unlock on new SIM" function for the people that is paramount to them to recover the device and they don't care at all if their data and passwords are exposed to the people that have found the phone. When the SIM is replaced it is clear that someone is trying to own your device. At this moment some people would like to continue searching for the phone and others would like to stop the new user finding their mails, passwords, account info, photos and all other personal information you might have in the device.