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Why buy a Faraday pouch for credit cards when....
Posted: April 26th, 2024, 3:35 pm
by stevensfo
...aluminium foil works just as well?
Years ago, I remember experimenting with a piece of alum foil and a card for a security door to find which part of the card had the antenna.
A thin piece of foil blocks the signal easily.
So why do people buy bulky Faraday wallets and pouches when you can protect your cards by simply slipping a few pieces of thin aluminium foil inside the wallet?
Steve
Re: Why buy a Faraday pouch for credit cards when....
Posted: April 26th, 2024, 3:40 pm
by simoan
stevensfo wrote:...aluminium foil works just as well?
Years ago, I remember experimenting with a piece of alum foil and a card for a security door to find which part of the card had the antenna.
A thin piece of foil blocks the signal easily.
So why do people buy bulky Faraday wallets and pouches when you can protect your cards by simply slipping a few pieces of thin aluminium foil inside the wallet?
Steve
Surely the effectiveness will depend on the signal strength. What range of signal strengths did you test with? At higher signal strengths aluminium might not attenuate the signal enough.
Re: Why buy a Faraday pouch for credit cards when....
Posted: April 26th, 2024, 4:04 pm
by Watis
I keep my car's proximity keys in a steel biscuit tin overnight.
I've just checked and found that, with the keys in the tin, the car can still detect them if the tin is within a foot or so of the lock.
So even that thickness of metal is not a perfect solution but hopefully sufficient when the tin is kept near the centre of the house.
Watis
Re: Why buy a Faraday pouch for credit cards when....
Posted: April 26th, 2024, 4:12 pm
by stevensfo
simoan wrote:stevensfo wrote:...aluminium foil works just as well?
Years ago, I remember experimenting with a piece of alum foil and a card for a security door to find which part of the card had the antenna.
A thin piece of foil blocks the signal easily.
So why do people buy bulky Faraday wallets and pouches when you can protect your cards by simply slipping a few pieces of thin aluminium foil inside the wallet?
Steve
Surely the effectiveness will depend on the signal strength. What range of signal strengths did you test with? At higher signal strengths aluminium might not attenuate the signal enough.
All I have ever used are security card detectors at work and occasionally the card reader in a supermarket. The card detectors beep with any sort of RFID card so came in useful when I was experimenting in removing the contactless feature of credit cards. Incredibly easy, though best to try with an expired card first.
I once wrapped my phone in foil and it didn't accept any calls, so I assume that the foil must work. However, I'm really interested in just the cards.
Steve
Re: Why buy a Faraday pouch for credit cards when....
Posted: April 26th, 2024, 4:17 pm
by stevensfo
Watis wrote:I keep my car's proximity keys in a steel biscuit tin overnight.
I've just checked and found that, with the keys in the tin, the car can still detect them if the tin is within a foot or so of the lock.
So even that thickness of metal is not a perfect solution but hopefully sufficient when the tin is kept near the centre of the house.
Watis
Could it be it's because your keys are actually in contact with the tin?
As far as I understand, the whole point is to have some kind of gap, a layer of plastic, rubber or similar between the object and the protective metal.
Otherwise, the tin may even be amplifying the signal?
Steve
Re: Why buy a Faraday pouch for credit cards when....
Posted: April 26th, 2024, 5:05 pm
by Gerry557
I think its more the wave lenghts of the signal and biscuit tin. Try earthing it.
Re: Why buy a Faraday pouch for credit cards when....
Posted: April 26th, 2024, 5:22 pm
by GoSeigen
simoan wrote:stevensfo wrote:...aluminium foil works just as well?
Years ago, I remember experimenting with a piece of alum foil and a card for a security door to find which part of the card had the antenna.
A thin piece of foil blocks the signal easily.
So why do people buy bulky Faraday wallets and pouches when you can protect your cards by simply slipping a few pieces of thin aluminium foil inside the wallet?
Steve
Surely the effectiveness will depend on the signal strength. What range of signal strengths did you test with? At higher signal strengths aluminium might not attenuate the signal enough.
No. A faraday cage is a faraday cage. There is no field inside it. You can be
sitting in your car when lightning strikes it and you'll be fine.
GS
Re: Why buy a Faraday pouch for credit cards when....
Posted: April 26th, 2024, 5:44 pm
by simoan
GoSeigen wrote:simoan wrote:Surely the effectiveness will depend on the signal strength. What range of signal strengths did you test with? At higher signal strengths aluminium might not attenuate the signal enough.
No. A faraday cage is a faraday cage. There is no field inside it. You can be
sitting in your car when lightning strikes it and you'll be fine.
GS
I know what a Fataday cage is. The only question is whether wrapping something in Aluminium foil generates one. tbh most people that think they need one would be better off making a hat with the foil and sticking it on their head.
Re: Why buy a Faraday pouch for credit cards when....
Posted: April 26th, 2024, 6:07 pm
by GrahamPlatt
Pretty much all you need to know on this subject (why buy cmmercial bags & not make your own)
https://www.mattblaze.org/blog/faraday/Matt Blaze, who’s he?
https://en.wikipedia.org/wiki/Matt_Blaze
Re: Why buy a Faraday pouch for credit cards when....
Posted: April 26th, 2024, 6:20 pm
by simoan
A very well known Cryptography researcher, if you move in those circles, which I used to. Ah, those were the days…
Re: Why buy a Faraday pouch for credit cards when....
Posted: April 26th, 2024, 7:03 pm
by DrFfybes
stevensfo wrote:Watis wrote:I keep my car's proximity keys in a steel biscuit tin overnight.
I've just checked and found that, with the keys in the tin, the car can still detect them if the tin is within a foot or so of the lock.
Could it be it's because your keys are actually in contact with the tin?
As far as I understand, the whole point is to have some kind of gap, a layer of plastic, rubber or similar between the object and the protective metal.
Would the biscuits not suffice?
Re: Why buy a Faraday pouch for credit cards when....
Posted: April 26th, 2024, 8:59 pm
by simoan
DrFfybes wrote:stevensfo wrote:
Could it be it's because your keys are actually in contact with the tin?
As far as I understand, the whole point is to have some kind of gap, a layer of plastic, rubber or similar between the object and the protective metal.
Would the biscuits not suffice?
It’s an Official Secret that the silent running of nuclear submarines is achieved using the sound deadening property of 11,856 packets of Jammy Dodgers,
Re: Why buy a Faraday pouch for credit cards when....
Posted: April 26th, 2024, 9:18 pm
by csearle
Watis wrote:I keep my car's proximity keys in a steel biscuit tin overnight.
I've just checked and found that, with the keys in the tin, the car can still detect them if the tin is within a foot or so of the lock.
So even that thickness of metal is not a perfect solution but hopefully sufficient when the tin is kept near the centre of the house.
Watis
My intuitive understanding of it is that the biscuit tin surface forces the voltage field along its plane to be zero. Same with aluminium, or a Faraday cage made of mesh so long as the gap between the wires of the mesh is not more than about 10 wavelengths of the signal in question.
That would IMV not preclude the cage from re-radiating an electromagnetic wave in such a way that the voltage field was perpendicular to the plane of the biscuit tin and in anti-phase with the electromagnetic wave within the tin impinging upon it. Maybe also the range limitation is a function of the polarization of the electromagnetic wave within the tin¹. So, for example, if most of the energy contained with the field hits the tin at an angle (highly likely) then only the component with the correct polarisation would get through.
Just my thoughts. Not really qualified. C.
¹ As propagation is reciprocal this would apply equally to signals entering the cage as exiting it.
Re: Why buy a Faraday pouch for credit cards when....
Posted: April 26th, 2024, 10:01 pm
by stevensfo
simoan wrote:DrFfybes wrote:
Would the biscuits not suffice?
It’s an Official Secret that the silent running of nuclear submarines is achieved using the sound deadening property of 11,856 packets of Jammy Dodgers,
If Blackadder had continued to the cold war, I can just imagine General Melchett (Stephen Fry) admitting as such to Darling.
Steve
Re: Why buy a Faraday pouch for credit cards when....
Posted: April 27th, 2024, 9:09 am
by Mike4
Watis wrote:I keep my car's proximity keys in a steel biscuit tin overnight.
Do you take the steel biscuits out first?
just curious...
Re: Why buy a Faraday pouch for credit cards when....
Posted: April 27th, 2024, 9:24 am
by servodude
Mike4 wrote:Watis wrote:I keep my car's proximity keys in a steel biscuit tin overnight.
Do you take the steel biscuits out first?
just curious...
https://trainsquirrel.com/products/steel-biscuits-t-shirt
Re: Why buy a Faraday pouch for credit cards when....
Posted: April 27th, 2024, 10:47 am
by stevensfo
simoan wrote:I know what a Fataday cage is. The only question is whether wrapping something in Aluminium foil generates one. tbh most people that think they need one would be better off making a hat with the foil and sticking it on their head.
tbh most people that think they need one would be better off making a hat with the foil and sticking it on their head. Actually, the reason I started thinking about it was nothing to do with aliens or Nigel Farage monitoring my brain or whatever. Simply that I read a comment from someone about how it was easier and faster for him to slip his phone into a light faraday pouch when travelling rather mess around with buttons. That got me onto protecting credit cards etc.
It also led me to a weird site in the USA about preppers/doomsday/ apocalypse loonies and how to protect your equipment from a massive EMP strike in a war. One comment asked about how best protect the whole house. I guess that any foil they have left over could be made into nice hats?
Steve
Re: Why buy a Faraday pouch for credit cards when....
Posted: April 27th, 2024, 11:22 am
by servodude
stevensfo wrote:simoan wrote:I know what a Fataday cage is. The only question is whether wrapping something in Aluminium foil generates one. tbh most people that think they need one would be better off making a hat with the foil and sticking it on their head.
tbh most people that think they need one would be better off making a hat with the foil and sticking it on their head. Actually, the reason I started thinking about it was nothing to do with aliens or Nigel Farage monitoring my brain or whatever. Simply that I read a comment from someone about how it was easier and faster for him to slip his phone into a light faraday pouch when travelling rather mess around with buttons. That got me onto protecting credit cards etc.
I wonder how his phone feels...
....stuck in its pouch trying to push as much power as it can into its RF front end because the world vanished... and hearing nothing in return, except the battery draining, in a futile effort to help the phone do what a phone does?
Actually probably just feels a bit warm?
Re: Why buy a Faraday pouch for credit cards when....
Posted: April 27th, 2024, 11:47 am
by Mike4
servodude wrote:stevensfo wrote:
I wonder how his phone feels...
A widely held view is that machines don't have feelings. My own experience contradicts this though.
Boilers for example, can be anything from moody, awkward and downright resistant to being fixed to delighted and co-operative.
Re: Why buy a Faraday pouch for credit cards when....
Posted: April 27th, 2024, 12:07 pm
by kempiejon
Mike4 wrote:My own experience contradicts this though.
Me too. As a confident grunt I can make "broken" kit work for me just by looking at it and treating it as if it's supposed to work. Users seem to struggle with this and are unable to reproduce the "broken" experience when I'm there.