Re: Why am I hearing beep beep beep?
I think it's mostly a matter of speed. The car needs a moment to shut off just like it needs a moment to turn on. If you are too fast on the draw (getting out, opening doors), you sometimes get a warning.
This may also happen if you try to lock a fob in the car (the trunk actually refuses to close if you try to lock a purse with a fob in it).
I think it also happens if you try to lock the car with another door not quite closed.
And, as you have mentioned, it happens if you have left something on.
There are also some alarms that can be turned on or off by your dash computer that may or may not have been accidentally changed.