On the other hand, folks get killed in evacuations due to false fire alarms too.
http://www.flightsafety.org/ccs/ccs_nov-dec02.pdf
In some of these cases, note that smoke detectors went off because the overpressurization of the cabin caused false alarms there. (Basically, the smoke detectors measure the absorbtion of radioactive alpha particles as this causes a drop in voltage across the air gap-- as particulates enter the gap or as air density rises beyond a certain threshold, the alarm will sound.)
Secondly, even in the case of an actual fires too it is important to ensure that folks are not evacuated into the fire, or spinning engines, or the like.