Keyless-entry keypads, those strips of numbers usually found near driver's door handles, are available on certain new car models, as well as from aftermarket suppliers. If you're looking at a used car with an original keypad-entry feature, it's most likely a Ford (or a Lincoln or Mercury). Many Ford vehicles have come equipped with keyless entry keypads over the past couple of decades, although a few other manufacturers also offered the feature for short periods in the 1980s and 1990s.
A code-based keyless-entry keypad is a convenient perk, much different from the more common remote-based keyless-entry systems that, when you think about it, really aren't keyless at all, since they require a key fob to be within a certain distance of the car to work. In contrast, the keypad doesn't require any sort of key or fob, just knowledge of the pass code. And if the pass code is lost, such as when the car is bought at auction or the seller's forgotten it, owners still have some options. For instance, the car still can be unlocked normally by using the traditional key.
But what if you want the freedom to accidentally, or on purpose, lock the keys in your new-to-you used car? A dealership technician can look up the original factory code or reset it using computer diagnostic tools. However, the dealership will probably charge you for this service, especially if you didn't buy the car there. (If you did buy the car at a dealership affiliated with its manufacturer, they should have either provided you with the code or reset it for you.)
There is another method for retrieving and resetting codes on some Ford vehicles. The vehicle has to be new enough to have "intelligent" keys (the kind with feature-laden key fobs), and you have to have two of them in your possession (so let's hope the seller of your car handed over all the keys). Use your owner's manual to locate the "backup slot" in the car's center console, insert the first key, and push the engine start/stop button. Wait a few seconds, and push the button again. Remove the first key, insert the second key, and push the button a third time. The factory keypad code should flash on the car's information screen. That code can be used to re-enter the car and to erase the personal keypad code, if the previous owner set one. From there, follow the code-programming instructions in the owner's manual [source: Ford].
If your used car has an aftermarket system (usually installed on the door or near the windshield) and the previous owner didn't give you the code, you might be out of luck. Your best bet is to contact the system's manufacturer for help — or possibly just remove it.