Cell phone door unlock trick just WORKED!!!

[BrianWC]

Okay, I was sitting there reading to my co-worker all the stuff on snopes and everywhere else that says that the cell phone/car door unlocker trick is a hoax. The lady in the office next door (who's very gullible) wanted to try it anyway. She called him on her phone and held up his remote to the phone. I don't know what her phone is but his is an ATT Blackberry Curve. And...it worked! It unlocked his trunk. I pointed out he was probably still in remote range so we turned off the phones and tried again. It DIDN'T work! What the heck? How is this possible? He's not a prankster. Matter of fact, he's telling my boss right now how it worked so I don't think he'd take the joke that far.....

BTW, the car is a brand new Malibu w/ OnStar. Don't know if that makes a difference...but.... Now the lady in the next office is going on how she knew cell phones were going to fry everyone's' brains.....

 

[brianl703]

The frequencies that cell phones use and the frequencies that car door keyfobs use are so far apart there's no way this would work even if the phones had the correct programming to allow it.

It's about 300MHz for keyfobs and about 850MHz or 1800MHz for cell phones.

Someone's pranking.

 

[drivewaytech]

I did this once with my company car. The car was in the front parking lot and someone stood in the back warehouse. Through the phone, they unlocked the doors and set off the alarm. They could not do the same without the use of the cell phone. However, when I got on the other side of town, I called the office and had them try again with the extra remote back at work. Needless to say, hopefully no one saw me on the parking deck holding a phone to the car door yelling "do it again!". It did not work. As far as explaining what happened when we were successful at work, perhaps the phone's antenna helps to boost the remote's signal.

 

[Footpounds]

This might work if car security systems worked via SOUND but as far as I know they don't. They use radio frequencies like stated above. Cell phones can't re-broadcast the frequencies used. I call "pranking" also.

 

[BrianWC]

Originally Posted By: brianl703
The frequencies that cell phones use and the frequencies that car door keyfobs use are so far apart there's no way this would work even if the phones had the correct programming to allow it.

It's about 300MHz for keyfobs and about 850MHz or 1800MHz for cell phones.

Someone's pranking.


No, I know it theoretically shouldn't work. I think drivewaytech's hypothesis may be the answer and the cell phone might have acted as a bit of an antenna for the keyfob transmitter. When we moved the car further across the parking lot, the trick didn't work. When we tried it with my saab remote, which is notoriously weak, it didn't work. But it worked repeatedly with the Malibu remote in a location where we repeatedly tried and failed to get it to work without the aid of cell phones. I suppose the only way to test this new hypothesis might be to hold the cell phone off but near the key fob.

 

[PandaBear]

For this to work you have to have a remote that works in the audio range. US cell are in around 1900Mhz, phone sound quality probably up to about 8Khz, if you all said that 300MHz is the keyfobs range, there are no ways it would work unless there is a codec translator on both side.

I'd seriously be worried if cell phone trick works, because that means someone can "wiretap" my alarm with a tape recorder.

 

[AcuraTech]

Even if it did work (it doesn't), holding it up to the lock cylinder makes no difference. The keyless entry receiver is generally buried somewhere under the dash, not in the door. I call [censored] on the whole thing.

 

[brianl703]

I'd think if anything the strong output of the cellphone's transmitter could actually cause reception problems for the keyless entry system's receiver. It depends on how well-designed the keyless entry system's receiver is.

 

[BrianWC]

Originally Posted By: AcuraTech
Even if it did work (it doesn't), holding it up to the lock cylinder makes no difference. The keyless entry receiver is generally buried somewhere under the dash, not in the door. I call [censored] on the whole thing.


Who's talking about a lock cylinder?


Look guys. I KNOW it's not supposed to work. That's my whole point. I was just wondering why it DID work. My guess is, like said before, perhaps holding the cell phone next to the keyfob extended its range a bit. B/C thankfully for me, who had told everyone at the office there was no way this could ever work, the trick did not work when we moved the car across the parking lot.

 

[Camu Mahubah]

Sounds like your bud had a hired ninja in the bushes with a key fob. When you moved car ninja asleep!

 

[javacontour]

The receiver in the cell phone is likely more sensitive than the one in the car, so it could pick up a harmonic of the original signal and somehow retransmit that signal (or a harmonic) to the cars receiver.

So while it may not be the original signal, there may be harmonic close enough to tickle either the cell phone and you are picking up something from the filter in the circuit, or the receiver in the car may be picking up the 3x or 6x harmonic from the phone.

Just guessing. Without any sort of RF scanning gear, it's all just speculation.

But "weird" things happen with RF

 

[Gary Allan]

Alright ..how digital super heterdyning? The output of the remote imposes its signal in some intermediate stage of the cellphone ..and that also gets carried to the other cellphone.

 

[BrianWC]

Maybe I'll have to bring out the scanner???? Yeah, RF is wicked. The morning after a cold front came through this week, on my commute to work, my CB reception was incredible. I was able to turn my squelch wide open and got no static, just layer on layer of transmissions. Pretty freaky....

 

[javacontour]

I think I'd try a different cell phone, such as a Sprint PCS phone or something very different, as well as another model of AT&T phone just to see if it's peculiar to that model phone and how it handles RF or if it's something common to many/most/all cell phones operating on a particular network.

I really think it's something to do with the mixer and/or local oscillators in either the cell phone, the remote receiver in the car or a combination of the two that allow the phone to pick up the remote signal with it's likely more sensitive receiver and somehow unintentionally amplify that signal or a harmonic and pass it on to the cars receiver.

 

[BrianWC]

Just to clarify, there were two phones involved. The phone next to the key fob was actually a Razr. The Blackberry was next to the car. So the Razr would have had the effect, not the Blackberry. I'm not sure what system the Razr was on, though.

 

[javacontour]

I don't think the phone closest to the fob mattered for my theory. You could try having the person using the phone closest to the car talking to someone on a landline either in the office or away.

I really don't think BOTH phones carried the signal. I think the phone nearest the car has a more sensitive receiver and picked up a signal the car couldn't get, amplified that signal, or a harmonic and that is what the car got and acted upon.

I don't think the signal was tunneled between the two cell phones. Telephone doesn't typically pass anything greater than 8KHz. If telephones could reliably pass greater than 8K signals, dialup networking wouldn't be limited to about 56K. If you could pass 300MHz over the phone, then you could get dial up internet at speeds as fast if not faster than cable modems.

So I doubt the phone nearest the key fob is playing a role in this.

It may be, but I doubt it.

 

[brianl703]

Originally Posted By: javacontour
The receiver in the cell phone is likely more sensitive than the one in the car, so it could pick up a harmonic of the original signal and somehow retransmit that signal (or a harmonic) to the cars receiver.


I'd think the FCC tests for that sort of thing, and engineers who design these things try to avoid it.

The consequences of retransmitting a harmonic of a signal it picks up can be severe.

Also, if it did, wouldn't it just oscillate? A big feedback loop.

 

[javacontour]

But do they not allow any retransmission, or have a limit. Standing less than 10 feet away from the car may retransmit enough to reach the receiver in the car.

They don't have to re-transmit at full power, just enough to reach the receiver in the car. I don't think the retransmitted signal is going to reach the cell tower.

 

[BrianWC]

To clarify, I wasn't thinking anything was transmitted over the phones at all. Just thinking the fob phone might have been the culprit.

 

[javacontour]

One could test that too by having the "fob phone" call a totally different number and see if the door is unlocked, etc.

Like I said, it's all just speculation at this point.