Today my client told me that her smoke alarm went off at 12:11 AM and it made me wonder why we say
"the alarm goes Off" meaning the alarm turned "ON"

Why don't we say the alarm is ON?
It seems that this is the case with every alarm, the house alarm went OFF, The car alarm goes OFF.

anyone else wondered about this?

Only when I'm parked in a driveway, or driving on a parkway.

Did you know in France thay sell snails as 'fast food?"

... and how can you go back before you go forth.

I suspect the alarm thing harks back to guns that do "go off" (at a similar dB level). I had a smoke alarm that went "off" about 5AM last night and almost resulted in the afore mentioned gun fire.
I couldn't get the thing open to get the failing battery out and it was chirping about every 10 seconds, until I hit it with my 24oz ball peen hammer. The battery came right out after that.

It actually doesn't go anywhere. It just stays where it is. So, more correctly, it suddenly stays on in the middle of the night.

I wonder if the saying could have originated from the noise from a kitchen timer turning off. When an oven or microwave timer turns (goes to) off it makes a noise.

To people there is no diffence from a timer running down to off or an alarm tripping - the beeping noise is the same.

Greg, your lucky it was a smoke alarm, I had a CO alarm start beeping at 3am last month.

With a smoke alarm if you don't see smoke or flame you know its the battery, it took me some time to figure out it was the "7 year replace me as I have expired" beep and not the call 911 / gas company alarm.

Standing in the cold in the back yard reading the manual with a flashlight to interpet the beep count I can do with out. I would gladly pay a little more for a photo cell on the unit to prevent the error warnings from tripping at night.

Are you going off on a rant?

no Rant at all. I was just wondering about that.

Greg,
I don't want to sound nasty or anything, but I've lost count of the number of times I've turned up with the Fire Service to a house fire where there are persons trapped only to find the smoke detectors had had the (failing) battery torn out.
This is one thing that really gets my goat, lives have been lost as well as a consequence, it also exposes our fire-fighters to an un-necessary level of risk.

Smoke detectors are installed for a reason.

I'll get off my soap-box now.

Trumpy, this is a backup to the backup. I have hard wired, multi station detectors in every bedroom and a bunch of loose battery only ones scattered around. This was one of about a half dozen in a 1600 sq/ft one level house. I had no problem going back to sleep with just the five.

She meant to say the "Smoke alarm activated"

Are you going OFF ON a rant?

It was a joke.
Granted it was a poor one.

Reno, there is no such thing as fast food in France, snails included! [Bloody horrid overrated things- a shrivelled black slug of gristle soaked in vivid green garlic butter- one more thing the Romans did for us. Ugh! Badger's noses anyone? ]
Two hours is about the norm in any eating establishment offering the usual multitude of courses. Even a trip to a local McDonalds has one ripping one's hair out in clumps, as they just don't get the concept. They always seem to cook the burgers on demand. Then deliver the fries to your table, as a second course, 10 minutes after the bun has disappeared down the cake-chute.

As to things 'going off', what about Microsoft's crazy 'click the start button' to turn off your pc? Doh!