When I was in HS, I accidentally set off the fire alarm in the old wing of the school.
I had a class in that wing (Computer Aided Drafting) and the fire alarm near my class had a plastic cover over it. I wondered what would happen if I opened it and as soon as I did, it started shrieking and there were flashing lights.

I completely freaked out and RAN out down the hallway a nd hid in the girls' bathroom on the second floor near my 2nd period biology class. I stayed in there for what seemed like forever and when I went back to class, there were a couple of teachers dragging a kid down the hall. He was protesting that he didn't set off the fire alarm and they didn't believe him.
I never told anybody (until now) that I was the one that did it.
TOV