Entering the key on the keypad is the "knock". The pilot is only alerted that there is someone outside if you enter the correct code. They then verify using eit

Entering the key on the keypad is the "knock". The pilot is only alerted that there is someone outside if you enter the correct code. They then verify using either CCTV or the peephole. If you just physically knock on the door then the pilot will be suspicious.