Conundrum

On the other side of the glass emergency-exit door, students mill about on the quad, talking, laughing, enjoying another perfect day in northern California.  I, however, take no notice, fixated as I am on the emergency exit's pushbar.  A colleague comes over.

--What's wrong?

--I'm not sure what to do.

--What happened?

--A little while ago, someone went out through this door, and the alarm didn't go off.

--OK.

--So I just re-armed the alarm.

--Right.

--The problem is, I was sure that the alarm WAS armed before that guy went through it.

--OK.

--So, now, even though I KNOW I just armed the alarm, how do I know that it will go off if someone goes through it again?

--Can't you test it?

--How?

--You want me to go through?

--But if you do that, and the alarm goes off, I'll need to turn the alarm off and then reset it again.

--Right?

--And then I'll be right back in the same situation.

--Oh yeah.  (Pause)  Well, what do you want to do?

--I guess there's nothing I CAN do.

--Guess not.  So, should we go?

--Yes, let's go.

We do not move.