I must admit I think a fire alarm may have been a poor choice for this experiment. Really, in all the fire alarms you've heard go off in your life - how many have been real fires and how many have been fire drills? Even the 2 I've been in that were real fires, I could have stayed where I was and not been affected in anyway. Obviously this is not always true but I think it is pretty much general experience. So what if they'd had a different sounding alarm and a voice saying "radiation leak, radiation leak, please evacuate the building" - I wonder how many people would have gotten up and left then?