Can You Unlock a Car Door With a Cell Phone?

Car remote key
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Locked out of your automobile? According to a viral message, you can have someone transmit a signal from your spare remote key via cell phone and unlock your car door in a pinch. Don't depend on it. While there are now apps provided by some carmakers and services such as OnStar that can unlock your car remotely, this method never worked. You can compare any post you see about it with the example.

Description: Rumor / Email hoax
Circulating since: July 2004
Status: False (details below)


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.


Comforting though it may be to imagine you can unlock your car door in an emergency by receiving a distant signal via your cell phone, it won't work. Your remote car key operates by sending a weak, encrypted radio signal to a receiver inside the automobile, which in turn activates the door locks.

Since the system works on radio waves, not sound, the only conceivable way a signal from your spare remote could be picked up by one cell phone and relayed to your car's onboard receiver by another would be if both phones were capable of sending and receiving at exactly the same frequency as the remote itself—which they can't.

All remote entry devices operate at frequencies between 300 and 500 MHz, while all mobile phones, by law, operate at 800 MHz and higher.

It's apples vs. oranges, in other words. Your cell phone can no more transmit the type of signal needed to unlock a car door.

Experts Weigh In

  • 03/14/07: Asked by WPVI-TV News whether using cell phones to remotely unlock a car door would work, Drexel engineering professor Bruce Eisenstein answers, "That's an urban legend, that's not true."
  • 04/01/07: Marcus Dacombe, head of product marketing and European sales for Nokia, fields a list of common cell phone myths for the International Herald Tribune. Of the claim that cell phones can be used to unlock car doors, the article says: "That is surely another trick the phone makers should have invente—except that the remote opening systems for cars work on radio waves, which cannot be transmitted over a cellphone."
  • 02/13/08: 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. Myth busted.
  • 05/02/08: WXPI-TV's Stacia Erdos tries the cell phone trick and finds it doesn't work. Pradeep Khosla, dean of Engineering and the CERT center at CMU, isn't surprised. "The remote on a car door works on a radio frequency," he says. "If somebody from other side clicks on the remote, what the cell phone will transmit is an audio frequency. The car will not recognize it. It's the wrong frequency."

Bottom Line

If your manufacturer has provided a phone app that can be used to unlock your car door, that is what you should use. If you have a service such as OnStar, they can be notified to unlock a car door remotely.

But you can't simply transmit the signal from your keyfob through a cell phone to unlock your car door.