OnePlus
Set a Lock Screen Password auf OnePlus
OxygenOS ships without an active screen lock by default on most OnePlus phones, especially right after a factory reset or a fresh setup. That leaves contacts, SMS messages, photos and installed apps open to anyone who picks up the device.
The lock method sits inside Settings ➔ Security & lock screen ➔ Lockscreen passcode. From there you pick Pattern, PIN or Password as your unlock method, enter it twice to confirm, and choose how notifications appear on a locked screen.
A Password gives you the widest character set and is harder to guess than a four-digit PIN or a swipe pattern. A Pattern is faster to enter but easier to observe over someone's shoulder.
The notification setting decides how much shows up before you unlock: full content, only that a notification arrived, or nothing at all. Choosing Show private content only when unlocked keeps message previews hidden from anyone glancing at the screen.
If you later add a fingerprint or face unlock, this passcode still stays active as the fallback method whenever biometrics fail.