The door should never be opened with anyone onboard the aircraft after an activation of the smoke warning.
If there ever was a fire... The halon may well of done its job, but halon does not have the ability to cool the embers... So as soon as the door is opened and a fresh source of oxygen is introduced you could have a very nasty surprise.
Much better for the door to be opened once everyone is off and you have a couple of firefighters at the ready with a jet!
Another reason to be carefull opening the doors...... the urban legends of various animals getting loose in the hold
