My 2008 smart 451 alarm sounds if I wait about 1 minute after locking ONLY when the key-fob is within range. If I lock the car, then walk far enough that I can't lock/unlock/panic with the key, the alarm will not sound. I thought it might be a defective button on the key, but I changed to the backup key and it does the same thing. There must be some signal the car is sending to the key periodically. What part (that I would replace) could possibly be causing this?