Bluetooth paired devices can be used to automatically unlock the LG smartphone by adding a trusted device that has already been paired via Bluetooth in the Smart Lock settings.

It doesn't matter what kind of Bluetooth device it is, it can be a Smartwatch, headphones, the car radio, fitness wristband or any other smartphone.

Note: To set the device as a trusted device, it must first be paired with the LG smartphone.

Android 9 | LG UX 9.0
Trusted devices -  Open the  Settings
Trusted devices -  Tap on  General
Trusted devices -  Tap on  Lock screen & security
Trusted devices -  Tap on  Secure lock settings
Trusted devices -  Tap on  Smart Lock
Trusted devices -  Enter  Password / PIN / Pattern
Trusted devices -  Tap on  Trusted devices
Trusted devices -  Tap on  Add trusted device
Trusted devices -  Choose desired  Device
Trusted devices -  Confirm with  Yes, add
  1. Open the Settings
  2. Tap on General
  3. Tap on Lock screen & security
  4. Tap on Secure lock settings
  5. Tap on Smart Lock
  6. Enter Password/PIN/Pattern
  7. Tap on Trusted devices
  8. Tap on Add trusted device
  9. Choose desired Device
  10. Confirm with Yes, add

LG Instructions