If you lock keys inside a car...

[TObject]

From the internet:

There has been a rumor going around in one of those dreadful e-mails that your friends and co-workers feel compelled to forward to you all the time. If you lock your keys in your car and you have a remote keyless entry system, you can get outside help to open the car if you have your cell phone with you. Just call someone that has a duplicate key fob that will open your car. Then, hold you cell phone near the door lock and have the person with the key fob call you back. The person with the key fob should then put the key near their phone and push the unlock button. The door should open.

I was skeptical, to say the least, about this rumor, and was about to dismiss it as one more Internet hoax. But I thought I better try it out first. Well, low and behold, it works. I tried it with both GSM and cdma cell phones, and it reliably opens (and relocks) the car.

I have been racking my brain for days about how this works. Two or more different wireless technologies are involved. I even used a 2.4 GHz cordless phone to make the call. The remote keyless entry usually uses on-off-keying (OOK), a form of ASK, to modulate a 315 MHz carrier with the correct serial digital code. Somehow the calling phone picks up this information and transmits it to the receiving cell phone, which then magically retransmits it to the door lock receiver in the car? Yeah, right.

All I can think of is that the digital code from the key fob modulates the sending phone and the receiving phone subsequently picks it up. But how does it transmit the code to the lock receiver in the car? Does the 315 MHz signal ride on the cell phone carrier some how? I thought I was a pretty good wireless guy, but this one baffles me.

Well, this doesn't work. How do I know? I locked my keys inside mom's Lancer. And asked my mom to use the spare keyless-entry fob over the phone.

I was very skeptical about the method, but with all the modulation-demodulation, carriers, sub-carriers the only way to be sure was to try it. And it doesn't work.

Funny thing, my mom tried to use my truck to bring the pare keys but the truck wouldn't start. I haven't used the truck for about a week, but it had been starting fine before that.

No problem I am getting this handled.

[mrblaine]

Originally Posted by TObject

From the internet:



Well, this doesn't work. How do I know? I locked my keys inside mom's Lancer. And asked my mom to use the spare keyless-entry fob over the phone.

I was very skeptical about the method, but with all the modulation-demodulation, carriers, sub-carriers the only way to be sure was to try it. And it doesn't work.

Funny thing, my mom tried to use my truck to bring the pare keys but the truck wouldn't start. I haven't used the truck for about a week, but it had been starting fine before that.

No problem I am getting this handled.

You should have had her record a little video on her cell of her pushing the unlock button and then shown it to the Lancer with a picture of the salvage yard in the background.

[TObject]

All back home safe and sound. I diagnosed the truck too, it just needs new batteries. It’s weird that both automotive mishaps happened on the same day. I was waiting for something else automotive to pop-up, for a trifecta… Not yet. Well there are still 51 minutes or so left until tomorrow. Maybe all transmission fluid will evacuate to the garage floor or something.

[speaceman]

"Did you press the button? Mom? The button. Did you press it. Press it. Press it. Did you press the button? Can you hear me now?"

"Never mind. I guess it doesn't work."

I shudder to think of my ever having to combine the technology of cellular phones with the technology of car fobs with the anti-technology of my mother.

[Jerry Bransford]

That old Internet myth is just that Sergey, a myth. Key fobs either use infrared (older) like a tv remote control or they use a small RF transmitter like a garage door uses. None of it is of course audible which a cell phone's speaker and microphone is limited to.

[TObject]

If electronic devices were perfect we would never had any audio hiss, bad TV picture, and you computer speakers would not be chirping while you are using your iPhone.

Electronic devices are not perfect and parasitic signals often propagate very far.

Yes. In the perfect world, this would never ever work. In the real world... I tried it, and it doesn't work.