My on-order Prius will come with the Smart Key System. I've never owned a car with so much as automatic locks, so I'm struggling to understand this new technology. For the fans, what's so wonderful about it? What is the care and feeding--how often do you have to change the battery? Is the battery a dealer only part? I've read elsewhere that cell phones might interfere with the operation of the Smart Key. Is that true, and if so, how far apart do they have to be kept?