Is an empty crisp bag a Faraday cage?

mickledore

mickledore

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Just seen the video of the car being stolen when the keys inside the house were zapped with some reader. We have been having a discussion about Faraday cages and it has been said that an empty crisp bag will suffice.

Any of you techy guys know if this is true?
If so would keeping car keys in such a bag prevent the scallies from using a zapper?
 
How about an experiment? Stick your phone in the bag and try calling it. Or put the keyfob in the bag and see if your car responds when you push the button.
 
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In very simple words…

The principle behind the Faraday cage is that though electricity
of very energetic nature, is quite a lazy traveller. This is a "force"
that always search not for the shortest path but the easiest one.
That explains why lightnings have so complicated designs.

A Faraday cage is safe as long as it presents — offers— easier
routes then what is inside.

A metallic (aluminium for ex.) could constitute a good cage BUT
it depends on the power of the current. Too strong, it could not
well resist the passage and other conductor may be chosen.

A crisp bag, if metallic, may represent a good protection against
light currents, some electromagnetic waves and infra-red remote.
In the case of lightwaves, no "holes" that could be penetrated by
given wave length.

A mosquito screen can be a good Faraday cage for low currents
but not for radio or IR signals.
 
Try it! FWIW, a single thickness of kitchen foil blocks the signal from my plipper - haven't got a crisp bag (or similar) here to try it. If the plipper's in my pocket and "hiding" behind the keys, it occasionally needs to be shifted to allow keyless entry and starting.
 
I hadn't thought of Pringles!!!!
Trouble SWMBO will say that a crisp bag/Pringles tube is untidy. Might have to be creative.
 
A nice silver tea caddy? (Go on - spoil her this commercialmas!!!)
 
Having had to work inside a one I can tell you that A common misconception is that a Faraday cage provides full blockage or attenuation; this is not true. The reception or transmission of radio waves, a form of electromagnetic radiation, to or from an antenna within a Faraday cage is heavily attenuated or blocked by the cage, however, a Faraday cage has varied attenuation depending on wave form, frequency or distance from receiver/transmitter, and receiver/transmitter power. Near-field high-powered frequency transmissions like HF RFID are more likely to penetrate. Solid cages generally provide better attenuation than mesh cages.
But as the device has a low power it would not be hard to screen it. many wallets nowadays have an RFID blocking compartment to protect your contactless cards.
 
You could also try a saucepan with a metal lid. Or a baked bean can.

But it's probably best to get a guarantee that the lock is secure, or demand a recall.
 
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ianp5a said:
You could also try a saucepan with a metal lid. Or a baked bean can.
Click to expand...
We have some 19th century black saucepans with lids that we use as ornaments. Could give them a try. Cheaper than Nod's silverware.
 
Just to put your mind at rest as a prolific eater of crisps, I've just tested the theory with an empty Walkers plain crisp bag which is metalised.

At 12 feet my car will open and close with the key very happily but put the key in the crisp packet and it won't do either.

Of course it could depend on the flavour of the crisps and whether they are crisps or corn snacks ( Cheesy wotsists ) or whether they are Smiths salt and shake but it is a starting point for further experimentation.
 
ChrisH said:
At 12 feet my car will open and close with the key very happily but put the key in the crisp packet and it won't do either.
Click to expand...
But will it open from two feet if the keys are in the bag? Could be that the bag is merely reducing, rather than totally blocking the signal.
More research needed - and crisp packets.
 
mickledore said:
But will it open from two feet if the keys are in the bag? Could be that the bag is merely reducing, rather than totally blocking the signal.
More research needed - and crisp packets.
Click to expand...

Or just use a piece of foil folded around the card?
 
I would suggest, purchasing a large multi-pack of crisps, to continue with experimentation. Every if it doesn't work, at least you have had a variety, of flavours of crisps :)
 
Experiments have proved that Walkers plain will only reduce the signal. At 3ft from the car the key will still operate the locks when fully enclosed in the packet. However above 3ft it totally blocks the key from working.
 
ChrisH said:
Experiments have proved that Walkers plain will only reduce the signal. At 3ft from the car the key will still operate the locks when fully enclosed in the packet. However above 3ft it totally blocks the key from working.
Click to expand...
What about putting two bags round the keys?
This isn't doing your (latest) diet any good.
 
I suspect that many people keep their keys just inside their front door so the miscreants can get within very few feet of them an probably have more powerful receivers than your car.
I thought these things were supposed to be a security device whereas they have turned into a convenience device. The signal should be necessary but not sufficient, ie a physical key should still need to be inserted in the lock.
 
ecoleman said:
Put your keys in your tin foil hat or move if it’s really a problem
Click to expand...


Yes it's a problem. As is the theft of kit from cars using signal blockers. It's happened (the latter) to at least four press photographers this year.
 
In fairness most of the devices used don't scan your keys they generate random or sequenced codes that are sent to your car. There is no need for the keys.
The miscreants walk past your car with a little box of tricks that transmits codes at a very high rate hoping they hit the right code within a few seconds. If they do they are in your car. By using another box straight into the odb2 diagnostics port they can either reprogram the main ecu to bypass the remote key or program a blank one.
Then off they drive.

The biggest aid to theft is people who leave their keys within fishing rod distance of their letterbox.
 
Crisp packets etc have very little effect on signal as they are still predominantly plastic. Besides your keys will get greasy and smell of cheese & onion (or whatever).

As an exercise: put your mobile phone in a biscuit tin, close the lid and call your phone. Assuming you are in an area of decent mobile phone signal, it will still ring.

Ok a phone is a much more powerful transmitter but the tin is also much thicker metal.

Keeping keys away from the front door or window reduces the chances, or just don't choose the keyless entry option when buying a car - keyless does seem to be easier to crack/bypass than a fob with a button.

The fobs with buttons are not invincible; they are still susceptible to jammers or code grabbers.
 
An empty crip bag is a good example of a poor crisp prison.
 
Don't these car-thieves' gizmos that transmit to key fobs only work with those modern type keyless ignition systems, which work by the car 'talking to' a keyfob/disk thing that the driver carries with them? If so, if you have a conventional 'point and press' type keyfob with 'old fashioned' ignition key then surely it won't work on them, as they rely on transmitting a signal, not listening for one and 'talking' to the car?

Surely the thief would need a scanning signal generator (grabber) instead for the old-fashioned point and press key fobs? Also, when they unlocked the car the thief would need the ignition key to operate the steering lock, unless they forced it and broke it, which will all take time?

Is there also the chance that a placing a 'keyless' fob in something like a metal biscuit tin might actually act as an antenna and increase the likelihood of it receiving a 'fishing' signal from a would-be car thief's transmitter? :confused:

PS I'm only asking these questions, not professing to know anything about modern car security... so don't blame me if your car gets nicked or your tinfoil hat doesn't fit, etc.! :D
 
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I have a point and press key fob that doesn't have a key to insert. It has a starter button. Once the fob is near the car it can be started. Doesn't gave to be in the car. And my car is 8 years old.
 
mickledore said:
Just seen the video of the car being stolen when the keys inside the house were zapped with some reader. We have been having a discussion about Faraday cages and it has been said that an empty crisp bag will suffice.

Any of you techy guys know if this is true?
If so would keeping car keys in such a bag prevent the scallies from using a zapper?
Click to expand...

What type of car do you have?
 
mickledore said:
Mine's an old C Max. No real value anymore - it's' on the list for scrappage if/when I trade it in. But that wouldn't stop the scallies from walking away with it.
Click to expand...

In truth, the scallies as you call them favour mercy or beamers.
I don't mean to diss your car but, the risk involved in stealing it probably outlays any potential reward.

I know how you feel though, my swift sport is keyless and push button start. I worry that people will steal my shopping when the car is parked.
 
I really don't care for the forum auto correct thing.
Can it be disabled?
 
My post number thirty six now makes me look like an illiterate retard.
Whilst that may be the case, I don't need help from a bit of code to prove it.
 
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