When an alarm goes off, people do not ask “what is going off”, they ask: “what is going on?” It gets worse. In buildings, you have to “set” an alarm system so that it will turn “on” whenever someone breaks a circuit causing the alarm to go “off”. With most other appliances, if you break the circuit, they will not remain on, and will not operate. This is particularly true with stereos, televisions, and refrigerators: when they go “off”, they will not make a sound.
But an alarm system is different somehow. Not only will they make a terrible racket causing innocent bystanders to want to find toilet paper, but the system that has gone “off” defies the meaning of the word by sending a signal through an open circuit that is “on”. It sends it to a security company some distance away. Once there, the signal in some instances turns “on” a flashing light. This alerts whoever happens to be gazing at it to pick up the phone and call somebody. That way, they can have a brilliant conversation with someone who would otherwise be sound asleep:
“Sir, the alarm is on in your building.”
“Huh? It is? Why?”
“I don’t know, but it’s going off.”
“Huh? How long will it take to go off?”
“It’s already going off right now.”
“Well, what do you need me to do?”
“You, or someone needs to re-set the alarm.”
“You mean I have to go turn it back on?”
“Yes, but first you have to turn it off.”
“I thought it was going off by itself!”
“It is. But that’s because it is on. Someone will still have to turn it off before you turn it back on.”
“If I turn it back on, will someone else have to come back down there and turn it off?”
“Only if you set it off.”
“So I’m to set it on?”
“Yes. But you have to turn off the alarm before you set it on.”
Alarm sirens and horns can put up quite a fuss. Personally, I think they are much more annoying when they are “on” than when they are “off”, but everybody is entitled to their opinion. By now, the burglar has had time to grab whatever he was after, and make a clean get-away. In the meantime, the police have been notified. If they have nothing better to do, they might want to ride by, and check it out.
But the police will not go inside where the burglar by chance could still be hiding until you go down there and turn off the alarm that is going “off”. That means you have to go inside before the police will. Even so, by the time the police get there (if they ever do), the intruder will have been long gone, anyway. And if the bandit was so thoughtless as to not remember to break a door or window while he was there, you will be charged between twenty-five and fifty bucks for a “false alarm”.
In quantum mechanics, you can have “off” and “on” at the same time. Maybe somewhere within that new-fangled arithmetic is some principle supporting alarm terminology, as well as the commonly used expression:
“Raise that window down!”
“There are more things to alarm us than to harm us, and we suffer more from apprehension than reality.” -Seneca (Roman philosopher, mid-1st century AD)