The mystery that turned out to be not one

This morning, as I was walking on the corridor, I noticed the lock on our classroom door, and suddenly I realized that the lights and fan were on. I was wondering who'd left them on, when I looked up and found a classmate sitting inside the room. I stopped on my tracks, to wonder how she'd  achieved the impossible feat. It was only when I turned and looked back that I realized that the other door to the room was open :) And since she was sitting closer to the other door, she hadn't turned on the other lights and fans.

Alas, so much for my mystery and thinking of Houdini...