One of the great advantages of modern cars is the keyless entry that is available thanks to key fobs. Whether your vehicle has automatic unlocking doors and pushbutton start, or you can just lock the doors from a few feet away, key fobs can be a huge benefit. But sometimes when these lovely devices stop working, it can be a huge hassle (and expensive to get one replaced). However, if you have been using the same key for a long time, you may not have an issue with the hardware, it may just be running out of power. But how do you replace the battery in a car key fob?