I've the standard alarm on my 98 phase 2 Spider (Black rectanglar plastic key fob, single button).
With the hood down the alarm will go off sometimes approx 5 minutes after setting it. It is always ok with the hood up.
Must be the movement sensors being rather senitive picking up sometime in the local vicinity around the car. However there is nothing obvious causing it around the car.
Does anyone know if there is a simple way of disabling the motion sensor part of the alarm from the standard fob remote? (Extra pushes of the button, etc??), but still have the doors, etc alarmed.