I am thinking the low battery might cause the key fob to send wierd signals. Either that or your lock button is jammed just enough to make contact. Try putting the key FAR AWAY from the car and way out of range.... see if that helps. A friend of mine couldn't figure out why his panic alarm kept going off on the car.... he replaced the battery in the key fob and all was ok.

FYI--- I had my key for 4 years. I use my car everyday and unlock the doors with the remote. I never changed the battery. I have a back up battery ready to go just in case.