Today, if you’re buying a new or fairly new car, you can expect it to come with a keyless entry system and a remote to control that system. The remote is often called a key fob because it is usually carried on a key ring. By definition, a key fob refers to anything worn on a key fob for decoration or functionality, but most of the time when this term is used, it refers to the keyless entry remote control. They have become as much a status symbol as anything else, but knowing exactly how they work can be very useful.
The key fob works like many other basic remote control systems. There is a computer chip in the remote that creates a very unique code that the receiver is programmed to recognize. You don’t have to worry about someone being able to reproduce this code, because a standard 40-bit rolling code chooses from about a trillion possibilities. Also, the code the system uses is not always the same and as a result the remote and receiver must be synchronized. This is done when installing the keyless entry system, so you don’t need to worry about it.
There is one problem that can arise from this basic design. If you press the remote and you are not close enough to the car for the receiver to pick up the transmission, the two are no longer synchronized. This problem is very easily solved because a typical system will have many other codes it will accept after desync (usually 256). However, this means that if you press the remote 257 times while out of range of the car, you may have a problem because the remote has no acceptable attempt codes left. In this case, you will need to reprogram the system; a process that varies by car make and model, but can usually be found online.
Finally, note that because this technology is so complex, the key fobs are not interchangeable and cannot be copied. You have to take good care of this little piece of plastic, because if you lose or break it, you’ll have to buy and program a new one. This can be an expensive process, but again it depends on the type of car you have. For some vehicles, you only need to follow a few quick steps, but for others, a professional mechanic (with the proper equipment) will need to do it. I would recommend checking online to see if you can program a new remote yourself as it will save you about $50-$100.