From what ive understood from another forum(I haven't had a chance to look it up in the manual yet), in the event that the battery is too weak in the fob to unlock the doors then you can use the manual key to get into the vehicle. The fob has a small transmitter in the end opposite the manual key, that has just enough juice in it to be able to start the vehicle. It is supposed to be physically touched to the push start button and should allow you to start the vehicle and get to wherever you need, to get batteries or get to the other fob, etc.