Could Of Gone Off?

Why do people say alarms go off?  I see and hear this all the time. 'The tornado siren went off'. 'Alarm bells were going off.' 'My alarm clock went off.' Don't they actually go on?  This is nothing new, by the way.  People have been saying something goes off, when it really goes on, for decades or longer.

When I was young, 'to go off' also meant to get upset or angry. This was generally used in conjunction with 'on', 'about,' or 'at'. Someone might say that  they were so mad,  they could've 'gone off on' someone, or they really 'went off at' them.  I am not sure if that use of 'to go off' is still in use.  If it is; then they might actually be saying 'could of gone off.' I see that a lot on message boards -- could of, would of, should of.  Then someone else corrects it with something like, 'It's suppose to be could've / should've / would've  (contractions of could have, would have, should have) . 

Of course, it's supposed to be 'supposed to', not 'suppose to.' At least that use to be ... er, used to be the case. By the way, I have recently noticed another meaning of 'to go off'.  It is used to indicate 'to go by'; to use something as a source. This is sometimes used with of, 'to go off of'.  If someone corrects someone else, they might say they are 'going off of' Merriam Webster.  

In case you did not notice, I am still unsure how one is suppose to use quotation marks in conjunction with commas, periods, question marks, colons, semi-colons or exclamation marks. We use to always put them last, after the punctuation. Now some say to put it directly around the quoted or highlighted part, before the punctuation. I guess there is no sense in going off about it.  It might depend on which source one goes off of. Still, alarm bells go off in my head. I wouldn't of written this if they didn't