Fire alarms

Hi! It was funny today, I was at my art class and my teacher was fixing a fire alarm that needed a new battery and after she put the battery in she couldn't get it back on. After fifteen minutes I walked over to see what I could do but then she got it. There was some writing on the plastic and I asked her what it said, she replied "I can't read upside down" so I stood there and made it out:

"Do not remove unless power is off"

oops....

-BF