You may enable passcode/password to protect your journals.
Go to Settings > Passcode > Enable Passcode.
- Simple passcode of 4 digits is used. You can disable to use a complex password making up of alphanumerics.
- Require passcode is set to immediately
- Touch ID is enabled, if supported on your device
This passcode protection is different from your device's passcode.
It is a second authentication to further protect your journals.