Sometimes this fixes "broken" ones too.

Did you know if you press any of your keyless remote buttons more than 256 times without the car in range, your remote will stop working until it's reprogrammed?

These things are fairly high tech, using something that is called rolling code technology.

For Technophobes such as Eric, here's the simple to understand version in a lot less words.

But get the simple instructions for your make of vehicle right here.