If the timer on the LG smartphone has expired, not only will the sound be heard but the device will also vibrate, and if the vibration is (not) desired, it can be turned on or off in the timer settings.

Android 9 | LG UX 9.0
Timer Vibration -  Open the  Clock -App
Timer Vibration -  Tap on  Timer
Timer Vibration -  Open the  Menu
Timer Vibration -  Open the  Settings
Timer Vibration -  Enable or Disable  Timer with vibration
  1. Open the Clock-App
  2. Tap on Timer
  3. Open the Menu
  4. Open the Settings
  5. Enable or Disable Timer with vibration

LG Instructions
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