This is an interesting concept. The problem would be that I see people lock their vehicle when they get out of their vehicle to put gas in it. Mostly little old ladies and the such. My co-worker told me she locks hers even though she is only going as far as the gas pump. Something about her safety or someone might steal her purse. I can't live like that, but anyways, these folks would never be able to put fuel in their vehicle if the fuel door locked when the vehicle was locked.