Todays useful motoring tip.

[mayevora]

Anyone ever locked keys in car (hard to do nowadays I know in modern cars) or lost keys while out and need to gain entry to car? Does your car have remote keyless entry?

This may come in handy someday. Good reason to own a mobile phone: If you lock your keys in the car or lose them and the spare keys are at home, call someone at home on their mobile phone from your mobile phone. Hold your mobile phone about a foot from your car door and have the person at your home press the unlock button, holding it near the mobile phone on their end.

Your car will unlock. Saves someone from having to drive your keys to you. Distance is no object. You could be hundreds of miles away, and if you can reach someone who has the other 'remote' for your car, you can unlock the doors (or the boot).

Pity it can't start the engine as well, but might come in handy.

Edited March 6, 2009 by mayesprit

[mangel]

done this and yes it does!!

[tinywillyuk]

Any techies out there want to explain how it works?

[molemot]

I've been thinking about that...!! I had assumed that the remote locking function was an RF link on the same sort of gigahertz band that all these remotes work on..but, if that's the case, how come it goes through the mobile phone system? It may be that the coding is being transmitted through the phone and it has sufficient power to work the door locks by swamping the system with much greater RF power than the normal keyfob. It's a mystery!!

[Jonathan]

Assuming this works (which I am doubtful but will try in a minute) the key fob transmits on 500mhz or something like that, phones are up into the 2.4Ghz band (I know someone will come on here and pick the exact freq down to the last hz but it's an example not science class...)

RF transmission works by modulating a smaller signal harmonic onto a larger carrier frequency (frequency modulation, there is also amplitude modulation), the effect is similar to when you call someone on a cell phone and hear normal voice, but move it towards a speaker and hear "derrrrdukderrrdukdukdukderrrrr" that is the raw signal coming into the phone, the phone is chaning that into comprehendable voice. The noise you hear on a nearby speaker is the RF being induced into the magnetic coil in the speaker.

The key fob doesn't 'speak' as such but the RF signal harmonic it gives off can be induced into the phone's carrier signal becuase the RF would get into the microphone circuit if held close enough (exact opposite of the "derrrrdukderrrdukdukdukderrrrr" effect) - that menas in theory the phone can be transmitting the code for the lock.

I suppose it's plausable that signal can be decoded by the receiver on the car desipte what frequency it's moduladted on - I'm off to try !

EDIT : Dont work

Edited March 6, 2009 by Jonathan

[mangel]

Never tried with Esprit as no remote locking!!

Impreza worked great though, from Ireland!!!

[Quicker]

this does not work. Cell phone transmit in the range of human hearing - not radio frequencies that the key fobs use.

http://www.snopes.com/autos/techno/keyless.asp

[Jonathan]

Hang on Toby says he's done it so there must be some truth in it. I would have thought modern alarms and C/lcoking wouldn't work but my main issue is the fact keyfobs are ~500mhz and cell phones are ~2.4Ghz. If you managed to modulate the code onto the cell phone carrier then it's probably a flook the thing worked.

Ultrasonic wouldn't work imo becuase the frequency of the sound would be disregarded by the cell phones compression.

I'm really interested to see if it does work and whether anyone can demonstrate it to me - I can think of a handy situation where I might need this

(all above board and legal mind you)

[mayevora]

Jon

I tried it this morning. Only from 1 mile away but it worked.

In all honesty, do you think I would have posted the thread if it didn't.

I'm not clever enough to work out how/why - it just worked for me on my mobile and using my spare key fob. (BMW Mini)

Edited March 6, 2009 by mayesprit

[Quicker]

this would mean that the cell phone's microphone and speaker can pick up and transmit RF......

[Mr_John111]

Absoutely fascinating.

I have no idea how/why it would work (or why it shouldn't) but will try it with my VW Eos. Perhaps we could post up here the empirical results of those applications that do work (and perhaps also those that don't)

[molemot]

Hang on a bit...these things are all DIGITAL, right? We're getting carried away with frequencies, when what matters is the digital information they carry. I suppose it's possible that the key fob can induce the digital information into the signal transmitted by the mobile phone, especially as there is no other signal, voice etc. at the point the keyfob is actuated. Then this digital information is transmitted through the mobile phone network, and duly arrives at the receiving phone..where, by the same mechanism Jonathan so succinctly describes above, the keyfobs digital information is induced into the car locking mechansim and ...bingo!...it's unlocked.

[Jukka]

We just tried this.

Rover 75 works but Discovery don't. Can't understand this.

[Hippo]

Apparently Richard and Judy rubbished this theory in todays Express...however they did say if you hold your keys up to you head you will get much better range...something to do with 'the gelantinous mass amplifying the signal, or possibly the cavities within the skull acting as an echo chamber'

Don't know about you, but I'M convinced...

I once tried the BMW Mini key from an absurd distance away (not using mobile phones) and it unlocked the car...so I'm still a little confused.

[peter_england99]

Worked on my car.

[Jonathan]

In all honesty, do you think I would have posted the thread if it didn't.

Woah there, I believe you've done it, but I've tried it with 3 different cars and can't get it to work.

If I could see it working I can perhaps see what I am doing wrong - I really want to see if this works.

Hang on a bit...these things are all DIGITAL, right? We're getting carried away with frequencies, when what matters is the digital information they carry. I suppose it's possible that the key fob can induce the digital information into the signal transmitted by the mobile phone, especially as there is no other signal, voice etc. at the point the keyfob is actuated. Then this digital information is transmitted through the mobile phone network, and duly arrives at the receiving phone..where, by the same mechanism Jonathan so succinctly describes above, the keyfobs digital information is induced into the car locking mechansim and ...bingo!...it's unlocked.

Yup, if this works, thats the only way I can think how it does it.

The biggest prob I have is how can a carrier at 2Ghz transmit a code into a receiver on 500Mhz....it's like tuning into channel 4 and wonding why you cant see BBC1.

All the debunking things I have read about this say it cannot be done but if a few people on here have managed it I'd like to know how - can can have all the 'experts' in the world say you can't do it and then someone comes up with the exception to the rule...

http://urbanlegends.about.com/gi/dynamic/o...one-remote.html

So you can see why there is some scepticism. I still think they are at the wrong end of the stick with audable frequencies etc - I still think the code can be induced into the cell phones carrier wave - however it's clear not all cars will do it and that probably depends on the type of alarm receiver and the transmitter encoder - if the encoder is not strong enough the code wont be induced into the cell phone.

I really wanna see this work !

[redshift]

Just because you are not speaking into your phone does not mean that there is no voice signal. Digital signals are never just 'off'. When there is no sound the vocoder that converts your voice to a data stream will output 'silence' data which looks just like voice data but the vocoder at the receiving end can decode this and generate no sound.

However, many mobile phones use a wideband digital modulation circuit that is mixed with another signal to create the transmitted output. It may be possible that the data signal from the keyfob is picked up by this wideband modulator and the data also gets mixed into the output.

Now consider the receiver part of your keyless car. Does it have significant filtering to protect against out of band signals?

Of course not, that would cost money. The RF performance of this item is probably worse that a chinese remote control toy car. Throw enough RF at it from a close mobile phone and all sorts of interesting cross modulation effects start to happen.

So as an RF R+D engineer I would say:

Is it likely to happen? - probably not

Would I be surprised if it did happen? - probably not

HTH

[lrg_machine]

Just tried this with a BMW Mini and couldn't get it to work over Vodafone with a Nokia 6300, are there specific mobile networks or phones this might work on?

I'd have thought the network carriers would be filtering out all other frequencies not required for the mobile anyway, so can't really see how this can work.

[Quicker]

for this to work -

the microphone of the sending cell phone would have to pickup the key fob's transmitted RF signal, convert it, send it to the receiving cell phone, which then decodes the signal and then using the speaker in the ear piece replicate the RF signal - right?

How can the microphone/earpiece possibly send and receive RF frequencies?

[Kimbers]

It is wierd, as it worked with the wifes car and not with my Honda.

Go figure!

[redshift]

How can the microphone/earpiece possibly send and receive RF frequencies?

It doesnt. As I said above, the modulation circuit in the phone is a very broadband device that will quite happily accept signals up to 1000 MHz and mix (add) them to the signal. The microphone wont react at all but digital RF signals are notorious for getting into other electronic circuits. Just look at how audio equipment reacts just before your phone receives a call for example.

[Jonathan]

haha pete, I came to the same conclusion !!

[Quicker]

http://www.dailymotion.com/relevance/searc...le-microon_news

[Jonathan]

Comically that has more use than the keyfob thing LOL

Amazing - I would not have bet that could work.

[lrg_machine]

What they don't show is the hotplate under the table.

We've also tried this one as well, with about half a dozen mobiles and nothing, so this one I think is rigged.