Can You Unlock a Car With a Cell Phone?

Car remote key
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Locked out of your automobile? According to a viral message, you can transmit a signal from your spare remote key via cell phone and unlock your car door in a pinch. Don't count on it, though. While there are apps provided by some carmakers and services such as OnStar that can unlock your car remotely, the cell phone method has never worked.

How this hoax got started is a mystery. A typical version of the email message purports to offer step-by-step instructions for gaining remote access to your locked car:

Subject: Unlock your car from the outside!
This only applies to cars that can be unlocked by remote button. Should you lock your keys in the car and the spare keys are home.
If some one has access to the spare remote have them telephone you on your cell phone.
Hold your (or anyone's) cell phone about a foot from your car door and have the other person press the unlock button, hold it near the phone.
Your car will unlock. I tried it and it works. Saves someone from having to drive your keys to you. Distance is no object.

The Truth About Remote Entry

It's certainly comforting to think that you could unlock your car in an emergency by sending a signal through your cell phone. Unfortunately, this method doesn't work.

Remote car keys (known as "Remote Keyless Entry," or RKE, systems) operate by sending a weak, encrypted radio signal to a receiver inside the automobile, which activates the door locks. Since the systems use radio waves, not sound waves, the only conceivable way a signal from your spare remote key could be picked up by a cell phone and relayed to your car's onboard receiver would be if the phone were capable of sending and receiving at exactly the same frequency as the remote itself. This is simply not possible. All ​remote entry devices operate at frequencies between 300 and 500 MHz, while all mobile phones, by law, operate at 800 MHz and higher.

In other words, it's apples and oranges. There is no way for your cell phone to transmit the type of signal required to unlock a car door.

Marcus Dacombe, head of product marketing and European sales for Nokia, fields questions about common cell phone myths for the International Herald Tribune. Of the claim that cell phones can be used to unlock car doors, he says: "That is surely another trick the phone makers should have invented—except that the remote opening systems for cars work on radio waves, which cannot be transmitted over a cell phone."

The Discovery Channel's "Mythbusters" tried—and failed—to unlock a car door with a remote signal transmitted via cell phone in a video posted online in 2008. The myth is officially busted.

The Bottom Line

If your car manufacturer has provided a phone app that can be used to unlock your vehicle, that is what you should use to open it. If you have a service such as OnStar, you can request that your vehicle is unlocked remotely. But you can't simply transmit the signal from your key fob through your cell phone to unlock your car.