It doesn't work when either door is open. I saw it quit, and at the time I was on the passenger side with the door open. However, the seat belt warning light does flash, and I do hear a buzzer when I start the car.
Being as it went out while I was working on the cell phone removal, I can't help but wonder if somehow I disturbed something or shorted something out. Again, it would have to be in the passenger footwell area.