If your car key fob was stolen, treat that fob as a working key until it has been removed from the car. It works for whoever is holding it the same way it worked for you.

Getting a new fob made doesn’t necessarily disable the stolen one. The stolen fob has to be erased from the car, and it’s worth confirming that it was. Once it’s erased, it can’t start the engine or unlock the doors electronically. The small metal key tucked inside most fobs is a separate matter, because it can still open the driver’s door.

What a stolen key fob can still do to your car

A fob doesn’t expire, and it doesn’t lock itself out after a few days. Until someone removes it from the car’s memory, it keeps working. What it can do depends on the vehicle, and a thief may have some or all of the following.

What reprogramming a key fob removes, and why to bring every fob you still have

Your car keeps a list of the fobs it will accept. One common way to remove a stolen fob is to clear that list with a programming tool and then add back the fobs you still have. The method depends on the vehicle. If you want more detail on the process, we’ve covered what key fob programming involves in a separate article.

On many vehicles there’s no way to delete one fob and leave the rest alone. The whole list gets cleared, which means a spare sitting in a kitchen drawer is erased along with the stolen one. It won’t work again until it’s programmed back in, so bring every fob you own to the appointment. Our fob programming cost guide goes further into what happens to old keys when a new one is programmed.

On some vehicles, starting the engine and the remote buttons are stored in two different places, and both have to be cleared. That’s why it matters to say the fob was stolen, so every function it had gets removed.

Once that’s done, the stolen fob’s electronic functions no longer work on your car. Its buttons get no response, the doors don’t unlock as it approaches, and the engine won’t start with it.

The metal key inside the fob still opens the door

Most fobs have a small release on the side or back. Slide it and a metal key blade comes out. It’s there so you can get into the car when the fob’s battery dies, and a lot of owners have never used it.

That blade is cut to match your door lock, and a door lock is mechanical. Programming only changes what the car’s computer accepts, so it has no effect on which key turns the lock. After the stolen fob is erased, the blade inside it will still open the driver’s door.

A push-to-start car usually has no ignition lock for the blade to turn. On a car that starts with a turned key, the blade may turn the ignition, but the engine shouldn’t run once the chip has been erased. With the door open, though, everything in the car is within reach. That can mean a garage door opener, the registration with your address on it, tools, or a laptop bag.

To stop the blade from working, the door lock has to be rekeyed or replaced so the old key no longer fits. It’s a separate job from programming, and it isn’t needed every time. Ask about it when you call.

After reprogramming, this is what has changed and what hasn’t.

Why a stolen fob is a bigger problem than a lost one

A fob you can’t account for and a fob you know was stolen tell you different things. With a theft, someone chose to take it, and they often took other things that point back to you. Think through what went missing with it, since that decides how quickly you need to act.

What to do first when your key fob is stolen

The hours between the theft and the appointment are when the car is most exposed. None of these steps disables the stolen fob. They make the car harder to find and leave less in it to take.

What to do if your phone key was stolen with the fob

Some newer vehicles let a phone work as a key. If that was set up and the phone went missing with the fob, the phone is a second key. Don’t assume its access was removed when the fob was programmed. Change the password on the manufacturer’s account from another device. Then remove the stolen phone or its digital key using the manufacturer’s instructions, which may be in the app, the account, or the vehicle’s own screen.

When reprogramming is enough and when the car door lock needs rekeying

Erasing the fob ends its electronic access, but the blade inside it still fits the door. How much that matters depends on what the thief knows about the car. If the fob was taken by itself, with nothing that shows your name, your address or the vehicle, the thief has less to connect that key to your car. The blade still works if they do find it. Rekeying the door lock is worth considering in these cases.

If the stolen fob was the only one you had, you’ll also need a new one cut and programmed. Our guide to replacing a car key fob explains how that works.

What to tell the locksmith, and what to check before they leave

When you call, give the year, make and model, say how the car starts, and say how many fobs you still have. Have the VIN, a photo ID and the registration or title ready as well. We work on Ford, Chevrolet, Toyota and similar makes, and we don’t service European vehicles. If a phone key was set up on the car, mention that too.

Before the technician leaves, test every fob you kept. Test one fob at a time, with the other fobs outside the vehicle’s detection range. If another working fob is close by, the car may be responding to that one and the test tells you nothing.

Testing your own fobs shows that they work. It doesn’t show that the stolen one was disabled, so ask which electronic functions were removed and whether the blade can still open the door.

Key Fob Stolen and Not Sure the Car Is Safe?