House Paint Foils Wardrivers

Ant writes "Security-minded U.S. decorators' supply outfit, Force Field Wireless, claims to have developed a do-it-yourself solution to the international menace of marauding geek wardrivers: DefendAir paint 'laced with copper and aluminum fibers that form an electromagnetic shield, blocking most radio waves and protecting wireless networks.' According to the South Florida Sun-Sentinel's report, one coat of the water-based paint 'shields Wi-Fi, WiMax and Bluetooth networks operating at frequencies from 100 megahertz to 2.4 gigahertz", while two or three applications are 'good for networks operating at up to five gigahertz.' However, there are downsides to this." Since it's a water-based paint, exterior use is only recommended for people who want more copper and aluminum in the soil surrounding their house.

Comments

Reminds me of a store my father once told me

[aardwolf204]

My dad was a war photographer in Korea. He had some level of clearance and once was working at a base on the coast of Florida photographing experimental weapons. He was walking around the facility and started talking to a major. The major was complaining about the fishing boats close off the coast, saying that they were known communist spies doing surveillance of the bases secret operations. The nature of the operations made them need to be outside and there was not much they could do about keeping the spies from photographing their operations from the fishing boats.

My dad suggested that they build a pipeline around the base and pump extremely hot water through it. The steam would keep the spies from getting clear photographs of the bases operations.

Ever been to the airport and notice that distortion coming off the top of the jets in the summer? The waviness is caused by the steam and heat coming from the plane. This is the basis for the pipeline.

The major had the pipeline constructed and shortly after the fishing boats stopped snooping around the base. Think of it as a photographic firewall...

Its not that OT when you think about it.

Interesting...

[gardyloo]

I'm not really familiar with wireless technology, but I DO know that a conductive shield around something will protect the thing inside it from extraneous electrical fields (as long as their frequency isn't super-high), but that any radiation produced by the thing inside the conductive shield will get out just fine. Because wireless things are on carriers of "only" several GHz, the increased size of the shield (as opposed to the normal antenna or whatever) shouldn't make any difference to phasings.
I guess that most people have their houses land-lined (or satellited, or whatever), and then use wireless networks to distribute bandwidth _within_ the house, right? Because putting a shield around such a house would only serve to keep outside signals from getting in, not inside signals from getting out. Of course, if protocols usually work with a "give-and-take" system, then this would cut off part of that, and people wouldn't be able to connect to your wireless system, but they _would_ be able to eavesdrop.

Re:Interesting...

[gardyloo]

It's not difficult at all. An electrical conductor will rearrange its free charges so as to make the potential within it a constant, and (+/-, depending on your gauge definition) grad(potential) gives your electrical field: thus, no field within an *empty* cavity within a conductive shield. (Can also be shown from Gauss' Law, and integrating around any closed loop which partially goes through the cavity, and partially through the conductor.)
However, if you introduce some non-zero field into the cavity (as, for example, introducting some charge through a wire from the ground into the house), the shield will STILL rearrange its charges to neutralize the potential gradient (field) within the conductor itself. But this rearrangement leaves surface charges on the outer surface, which act as just a "distributed" version of whatever charge is in the cavity.

Your argument is one that undergrads love to use on their professors, but the uniqueness theorems of electrostatics render it null and void. There IS a significant difference between the "inside" and "outside" -- inside the shell, any field line is guaranteed to terminate on a piece of shell; outside the shell, only a tiny subset of field lines have to terminate on the shell -- the others can go to infinity without ever hitting a conductor. (But see Feynman's and Wheeler's arguments about radiation reaction forces for a somewhat more complicated explanation.)

Re:Interesting...

[Anonymous Coward]

For a mathematicians version of this proof, consider this: when you paint your house in laced paint, are you enclosing your house or the rest of the universe? =) The two are equivalent, and hence, if you're transmitting from inside your house, you are *outside* the protected universe, and your signals can't get there.

Re:What about cell phones

[drgonzo59]

Or perhaps in movie theatres, but then jamming would be easier than painting I think. Also, doctors or any person who has to be on-call might object to that.

Actually no...

[Svartalf]

It would be good Tempest hardening for a SOHO or a SME type business where you didn't want the signals getting out of the building. And I can see some locations going for this as part of their Tempest shielding regimen.

Radiation in a reflective cavity.

[goombah99]

This could also create problems too. past studies have noted that cell phone intenisty inside subway carriages can be 100 fold higher due to resonant trapping of the energy. Edge effects could be even higher. Like wise there will be reflections creating nodes in your house. Since the wavelengths are quite long these nodes will be macroscopically large.

Notably, the corners of your house will act like corner cubes maximally reflecting the energy back to the emitter itself. If the emitter happens to be your laptop then you are going to get the majority of the radiation passing through you on each round trip bounce.

as it happens, the wavelength is near the wavelength of your microwave. The microwave is tuned to optimally excite the rotational frequency of aqueaous water. The 2.4 Ghz is slightly off the optimum but You are inhogenous enough that you probably absorb quite well in this region. The rest of the dry materials in the room wont be doing much absorbing. Thus you will become the primary fate of all the radiated energy.

so you lose on two accounts: 1) high field strengths 2) all the energy resonates around till if finds your testicles.

Brains! Brains! Brains!

[dbIII]

Or are we all disoriented and stricken with alzheimers due to the aluminum

Here's an interesting bit of trivia about the early alzheimers research: it compared fresh brains from a control group with brains of sufferers that had been preserved in an aluminium sulphate solution. For years people were trying to work out how we could possibly metabolise aluminum (it take serious chemicals, heat and electricity to extract it from alumina) until someone took a look at the orginal study and tracked down the contaminant.

The more stupid the mistake the less people want to admit it - it took many years before aluminium was ruled out as a contaminant, but since the aluminium link had been in the newspapers for years we are stuck with another urban myth (just like the wartime carrot nightsight myth - you can't magically boost you night vision with carrots (Mawson didn't get better vision fron a near lethal dose of vitamin A), but it was the excuse to avoid admitting that radar existed in WWII).

Re:What about cell phones

[boaworm]

WHY do teachers NEED to carry cell phones? And even if that was the case, they could be wearing simple wireless phones connected to the landbased phone system, the signal should stay within the building...

I had other things in mind though. All those people who are afraid of the new 3G frequencies and the problems that can cause, can we simply not paint their houses?

Or this discussion we had a while back about amish people not allowing cell phones. What a great opportunity for them.

So, the last question is.. what happens if i put this paint one a cell base station. Can i simply drive by and spray a station, and render it inoperable?

insulated walls

[pair-a-noyd]

My dad insulated the walls of his garage with Styrofoam with a foil backing. His 900mhz phone doesn't work in the garage now.
He tried running a wire from inside the garage to outside of the garage thinking it may carry the signal, but that didn't work very well.
He tried moving the base station to the upstairs of the house but the sheet metal roof blocked it from that angle too.

MOST new homes are now constructed (around here) with that foil backed styrofoam. Seeing the trouble it made with a 900mhz phone, I would think it cause just as much trouble for other signals. It's solid so I would think no wavelength should be able to penetrate it except by sheer brute force, IE a "hot" signal.

Re:What about cell phones

[arivanov]

IR shielding on more expensive glass does it already. Painting the doors is also a bloody good idea and I have alluminized floor underlay already (saves you up to 20-30% of heat loss through the floor). T

Actually, they are marketing it the wrong way. They are marketing it as means of signal not getting out. I think the case of signal not getting in is considerably more interesting.

Which leads to the nice and obvious results. The idiot neigbour with the new and flashy access point he got for Xmas is no longer interfering with your wireless.

While at it, alluminium laced paints are usually highly combustible. What is the fire safety rating of this stuff?

Re:Useless for general population.

[advocate_one]

Don't knock it... something like that would be ideal for coating the insides of tents etc. to quickly create "secure" processing areas. And if anybody's wondering about patenting that idea... forget it... it's already patented. My brother holds a patent for doing that very same thing with his own special goop...