My '08 will beep the horn several times to indicate that a FOB is still in the car if I close the drivers door and then walk forward beside the left front fender. That appears to be close enough to the car for it to think that the FOB in my right pocket is inside the car. If I walk away a little farther from the fender, this does not happen; or if I pause for a couple of seconds beside the door before walking away.
My '06 does not seem to be this finicky.
How did I notice this? When I park the '08 in the garage and my wife's '06 is also in the garage, there isn't much room between the cars, so I end up walking close to the front fender to leave the car. When my wife's '06 is not there, I give it a wider berth and no beeps.