Talking about projector equipment in school, my high school had record players and independent film strip projectors. You'd play the associated record, and when the record beeps, the kid running the projector would advance the filmstrip one picture. One time, the guidance dept had the entire senior class in the auditorium, and they had some lame filmstrip presentation about selecting colleges to apply to. Some of us were able to reproduce the beep well enough to trick the kid to advance the filmstrip early, and thus we'd run out of pictures before the record presentation was done...