Fixed your post
I'd do it like this:
Four
trigger_multiples bordering the hacker-leaving area in a hollow square shape, and a
func_button or whatever to act as the hacking control. Have the _multiples targetting a
trigger_relay, state off, and the _relay targetting the
ambient_generic for the alarm sound (and any other entities for during-the-hack).
Then set the button to target another _relay, trigger state on, and set that up to target everythin' else.
Should work, if not, there're other, similar ways, and you might be able to adjust this method. You might also do well to look at SlayerA's example map,
Hold-Open Door.
Hope that helps; good post b'th'way.