If the battery is getting low in the car remote key (or garage door remote), and it does not open the door when you point it at the car/roller door no matter which orientation or position you hold it, this is what I do:
Hold the remote upright under my chin and open my mouth, and it opens the door. In fact I find this method work at a greater distance than just pointing the remote horizontally, directly at the car/roller door. It works every time without fail.
I assume is has something to do with creating a chamber with your mouth??? amplifiying the RF?? Don't ask me to explain it, but I've been doing for for years (yes, I should just change the batteries!
)