The Knock Code security feature is a unique unlocking method on LG devices which lets you unlock your Android by tapping the screen according to a pattern. To setup and enable Knock Code on LG G4, do as follows:
1. Open the Settings application and move to the Display tab
2. Under the Home & Lock settings, tap the Lock Screen option
3. Now under the Screen security settings, tap the Select screen lock option
4. Select the Knock Code option from available unlocking methods
5. Read the instruction and set your knock code, by tapping the screen from 4 to 8 times to setup a pattern tap.
6. Enter your knock code again and provide an alternative PIN (in case, something goes wrong), and specify what type of notifications you want to get on lock screen; show all, hide sensitive, hid all
7. And you are all done and you can unlock your G4 by just tapping according to the pattern