On my 2006 RL, the red security system light flashes and is visible from outside the car when it is locked. That is expected. But why does the light flash when I am sitting in the car (I have just unlocked) but before I turn the ignition on?

 

I believe because it is active until an authorized key is detected and you have initiated ignition. The car detects the key when you go to open the door but I do not believe it continually 'pings' the key so the next time it 'checks' for authorization would be when you go to start the vehicle.