We have them once a month, and I always dread that day. Last time we had it in fifth period (I have choir that period) and we were about to sing a lullaby type song and we get the crap scared out of us by the fire drill DX
It's usually on the last Monday of the month, and I'm bracing for it. Once the alarm goes off and I have the crap scared out of me, I'm alright.... until the last Monday of next month.