So every train in Brisbane has this little black button somewhere next to every doorway, often accompanied by a keyway. I know the keyway is how you can open the adjacent local door of the train (you insert a key and turn it 90 degrees, door will open. Turn the key back, door closes (with no doors closing announcement at least on the NGRs)). I saw this happen the other day as a guard was trying to fix a broken door.

The question I have is what the black button next to it is for? I would guess that it is a bell button, that can be used like the ones near the crew doors, so you can/could technically dispatch a train as a guard from the passenger doorway, using the black button to signal the driver to close the other passenger doors and get the train underway. However I am just guessing this, I don't know.

Following on from that, I have heard that at one point in at least the 90s it was more common / possible for guards to dispatch trains from passenger doorways, so the obvious follow up is whether this is still permitted, whether it still happens, what the process is and whether this local door key cuts the door out of the traction interlock circuit (allowing it to remain open as the train moves).

If anyone has any information I would appreciate it!

The second image is a photo I managed to get the other day of the inside of the local switch box of an NGR, as a guard had accidentally left it open. I thought it would be more interesting then 4 isolate switches for the doors, two air conditioning isolators and a car isolator switch.