Back in the days when I was a teacher, there was a time when the fire alarm would got set off about once a fortnight. Cue whole school getting evacuated and a fair chunk of the local fire brigade turning up...
Everyone had it down as one of the lads setting them off 'for a laugh'. Until, after nearly two terms of this, the culprit was caught in the act. Turns out it was one of the quiet, wouldn't say boo to a goose, Y9 girls.
Why was she doing it? Liked ogling firemen...