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Recently I have heard that somebody locked up keys inside the car while on vacation, so after calling family back home, asking them to use spare keys unlock button close near the phone, so that other phone near the car manages to unlock the doors.

After hearing this I have tried with my coworkers and manage to unlock some of the cars via phone, but not every car on the parking. So it seems that this is not just a myth as I thought at first. I would like to know why is this possible. I doubt that you can record radio wave with the microphone and then play it as unlocking signal...

How is phone able to transmit radio wave signal?

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  • Welcome to Motor Vehicle Maintenance & Repair! Sep 6, 2023 at 11:54
  • Which car remote successfully unlocked doors? Most basic remote start systems have a range of about 1,000 feet/305 meters, though a few starter systems provide an extended range of 2,000 feet/610 meters. Vehicle manufactures bundle subscriptions of their vehicle cellular system to remote Lock/Unlock/Start with hvac preselct temperatures to individual cellphones with an app and provide vehicle location. In theory, a vehicle with cellular remote start can be operated from anywhere in the world with cellular services.
    – F Dryer
    Sep 6, 2023 at 19:07

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I'm not sure how that'd work, because a phone only transmits/transfers sound, not electromagnetic radio waves which you'd find being sent out by a remote. Mythbusters even did a piece on this calling it busted. The voiced speech of a typical adult male will have a fundamental frequency from 85 to 155 Hz, and that of a typical adult female from 165 to 255 Hz. Car transmitters most commonly use a frequency of 315MHz in the the U.S. and Japan, and 433.92MHz in Europe. There is no way a cell phone is going to pick this up audibly, then retransmit the signal at the other end. Not only can it not "hear" the frequency coming in, it can't recreate the signal at the other end. If you were able to unlock/lock a car in a parking lot, I'd suggest the reason was you were still close enough for it to pick up the signal as it normally would ... ie: you weren't far enough away from the vehicle.

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You said:

After hearing this I have tried with my coworkers and manage to unlock some of the cars via phone, but not every car on the parking.

Let me guess how you did this: Your co-worker gives you their remote and goes outside to the parking lot to stand next to the car while you remain at the office window. When your co-worker arrives at their car, they call your phone, you answer, and you press the Unlock button on the remote while standing at the window. The car door unlocks.

To discover why this happens, repeat the experiment with no phones. If a car unlocks with a phone, it will unlock without a phone. The phone has nothing to do with it. You are unlocking the car by direct radio transmission from the remote to the car. It helps that you are high up above the ground clutter to help increase the range of the remote.

So there is nothing mysterious here: some remotes work at relatively long distance within line of sight, some do not. The phone has nothing to do with it.

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  • Well, I believe that mobile phone antenna perhaps amplified unlocking signal. It wasn't really done from the window, but rather through window and 2 walls and some distance. Also need to mention that locking didn't work. But tomorrow we gonna try to unlock over much greater distance like 2 kilometers.
    – adict
    Sep 6, 2023 at 13:48
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    @adict - If the phone was actually transmitting the signal, it would work either way. I agree with MTA in that I think it was a fluke and the car was getting just enough signal to do the action. Really, the phone has nothing to do with it. Sep 6, 2023 at 13:57

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