The car will also beep when you arm it if you hit the arm button before the inside lights dim down and off. I noticed this one day. If you wait for the interior lights to dim down and turn off like they usually do before you hit the arm button it will not beep. But if you hit the arm button to fast BEFORE the interior lights go out it thinks that you left a light on, like the dome light or thinks that the doors, trunks and other stuff is still opened.
