Disable biometric logins and enable a passcode.
Enable encryption. Most Android and Apple devices will do this automatically when you enable a passcode or biometrics, but double-check in the Settings menu.
Remove unnecessary apps and reinstall them later. Even when not in use, some apps can send and receive data. This can slow down an already spotty connection and could be used to monitor your activity.
Log out of any apps you won't need. By default, you usually need to log in to an app only once to use it, which can be a problem when you're not in control of your phone.
If you back up your phone (and you should), make sure that your backups are secure with a complex, unique password and multi-factor authentication. This may require making changes to your Apple or Google accounts. To help you get started, see our guides to backing up iPhones and Android devices..
Enable the remote-control features built into Android and iOS so you can wipe or disable a lost or confiscated phone remotely.
Use secure messaging, and set text messages to delete automatically. (More on this below.)