You can use Google voice search function provided by Google.
You can execute mobile phone features using LG Voice by pressing the Call button when using a Bluetooth headset.
How to use Google voice search
Select Voice search in the Google folder or touch the Google voice icon on the right side of the Google search bar.
If you select "Settings > Schedule > Google > Search and Now > Voice > OK Google detection > Always use", your voice will be recognized the moment screen is turned on or off, or while mobile phone is charging.
How to use LG Voice
Register the Bluetooth headset that features using microphone function by going to: Settings > Network > Bluetooth menu. Press the Call button on the headset and speak a voice command to activate desired function.