Meaning, no false alarms. Set the thresholds such that it doesn't go off for undetectable or even very minor quakes.
With only seconds to act, people need to feel confident in reacting without a second thought. If the alarm sounds and the teacher says "Hmmm, let's see if it's really a big one before taking cover." then it's lost some of it's usefulness.
Same with the automated stuff. It would be unfortunate to get to a point where the alarm goes off and doors roll up, gas is cut off, etc and people immediately think "Crap, not again. Now I have turn the gas back on and close the damn doors."