Originally Posted by
Waterhorse
It has been a while since I flew the Airbus but it used to be a slider on the front toilet door which the pilots had to check using the CCTV. It was a pain in the neck both figuratively and literally and was introduced post 9/11 as a temporary measure. I think the newer delivery Airbus aircraft have the button so there is a mix of ways of giving the cabin secure.
The BA ones all have sliders on the toilet door, the ex BMI ones have a button that we press either on a panel (older version) or on a screen.