Android menus vary a little between phone makers and versions. Use Settings search if a label in this guide is named differently on your device.
1. Set a secure screen lock
Open Settings and search for Screen lock. Choose a PIN or password you can remember but that is not a birthday, address or repeated number. Set the display to lock reasonably quickly when not in use.
2. Turn on Find My Device
Make sure you are signed in to your Google Account, location is on and the phone can connect to the internet. Search Settings for Find My Device and enable it. This can help you locate, secure or erase a lost phone from another device.
3. Check theft-protection options
On supported Android versions, go to Settings → Google → All services → Personal & device safety → Theft protection. Available features differ by device and Android version. They generally require a screen lock, so do that first.
4. Keep Android and apps updated
Open Settings → System → System update and install updates when practical. In Google Play, update apps from your profile menu. Updates can fix security problems as well as bugs.
5. Install carefully and review permissions
Prefer Google Play and the official sites of trusted organisations. Avoid apps that promise free paid features, “cleaning” miracles or a prize. In Settings → Privacy → Permission manager, review which apps can use your camera, microphone, location and contacts. Remove access that does not make sense.
If the phone is lost or stolen
Use Find My Device from a different trusted device. If you believe the phone is stolen, avoid confronting anyone. Contact your mobile provider to secure the SIM and change important account passwords if you suspect somebody had access.