An Alarming Ability

(I am taking a history class with a world-famous historian. Most of us have taken multiple classes with him and he has specifically asked us to take this class. We view him as a minor deity. One day during class the fire alarms go off.)

Professor: “I guess we should evacuate.”

(Twenty minutes later it is clear it was a glitch in the alarms, so we go back to class. Five minutes later the alarms go off again.)

Professor: “STOP.”

(The alarms immediately stop.)

Professor: “I can do that.”