Silverpie -
I believe that the arming of the doors is one of the things that is checked when the command "Flight Attendants, please prepare your doors for departure and crosscheck" is given over the PA.
The airlines have different announcements for the same thing: some airlines use the PA announcement: "Flight Attendants, doors to Automatic" (maybe LH?) to tell them when to arm the slides.
There have been instances where someone accidentally opened a door with the slide armed - makes a huge mess, takes the a/c out of service, it's expensive to repack the slide, and I think that it's even happened at a jetway before, doing fairly substantial damage.
Greg
[This message has been edited by greg99 (edited 05-26-2000).]