We got 100 comments on the silly Snowden Sack… Which was a 100% failure. Or so I thought. I did some testing, and it turns out I’m probably going to be able to redeem the mylar Snowden Sack! Here were various tests:
- Put phone in all clad pot with lid: Didn’t ring.
- Put phone in Snowden sack. Rang. Tie to get a better seal: Rang.
- Put phone in all clad pot, covered with an el cheapo disposable aluminum pie plate. Rang.
- Wrapped phone in left over torn aluminum foil. Rang.
Things were looking bad. So, yesterday, when Jim left for New York, I went out and bought provisions which included heavy duty aluminum foil. Then Jim’s flight was cancelled, he came home, tests were delayed. Tests were resumed this morning.
- I wrapped the phone in 4 layers of aluminum and folded to create a seal: Phone did not ring.
- I progressively unwrapped, testing with 3, 2, 1 layers, each time taking care edges were sealed. Phone did not ring.
- I retested doing a “bad” job by not folding over the edges to seal: Phone rang. Clearly, the sealing at the edges
I did a number of tests sealing “well” and “fairly badly”, and concluded that imperfections in sealing were a big issue. I know some of you guys already knew this. But anyway, as a practical matter, if I very carefully smooth the foil and press the edges to get very good smooth contact, that seems to be “good enough” for this phone. I don’t seem to actually need to fold the edges of the foil over on itself.
But if I just wrap the phone and don’t take pains to press the foil very, very firmly leaving even a tiny gap, the phone rings.
So, then looking at my Snowden bag, I thought… maybe it’s the seal? I then got the brilliant idea to fold over the edges on the Snowden sack:
. The phone did not ring. I retested a few times: The phone does not ring provided I am very, very careful to make sure the edges stay well folded over. If I don’t hold the fold over edges carefully to make sure they truly fold, it rings.
I’m not absolutely positive this is due to the “folding over”. There is a possibility that mylar is just boderline effective. But it at least appears the issue is not the mylar, which seems to attenuate sufficiently for this puny phone operating in my kitchen. But clearly the seaming at the edges is not insufficient because the bag never works if the side eges aren’t folded over. Knowing this permits me some ideas I can test out. After all, my design criteria are
- Pretty easy to sew.
- Use cheap lightweight left over material I already have at hand. (As opposed to ordering materials that may or may not work.)
- Easy to stuff phone into pouch.
- Attenuates sufficiently to interfere with communication with local tower.
- Fits phone.
For now, I’m going to go upstairs, cut some scraps and bind the edges with mylar backed fabric. (I had cannibalized and just used a think single strip of blue fabric laid over two pieces pressed together )
This thing is going to get very ugly before the final halfway decent design exists.
Violating the materials-at-hand rule, there are some widely-available materials that may work:
1. Put a layer of aluminum foil between cloth. “Fusible interfacing” is available at most fabric shops, and when heated with an iron will fasten some materials together. This says it works on aluminum foil: http://www.kobakant.at/DIY/?p=2529
2. Seal with two rubberized magnetic strips. In case this material does not block radio, wrap aluminum foil around strips. Don’t cover with cloth.
However, keep in mind that all these materials are subject to wear. If the mylar or foil wears “too much”, you can leak radio signals. There are tattletales which you could put on the outside of the bag to report leaking signals, but that means that you have to put your purse in a charger to power the RF-detection devices.
Go see “Red2” and watch the the John Malkovich character. He would be very excited the possible uses of tinfoil.
lol.
Lucia, I could have told you that. My custom made and form fitting tin foil hat secures my cell phone every time.
I do have to be careful to avoid the antenna sticking out.
hunter,
It turns out I don’t need the tin foil.
My next step was to just try an outer bag and inner bag. It works provided I make sure flaps are closed. It works every time. No fiddling.
So, I’m pondering a double fold-over design. I want something very easy that a user can’t screw up by not closing properly.
Kenneth–
I think what I’ve discovered is a tin foil hat won’t work because of the large hole you need in order to stick your head into the hat. You need a tinfoil jumpsuit of some sort. I’m not sure how you can make provisions for eyeholes.
You may be deft enough sewing that it makes no difference, but I would experiment with a few variations using prototyping adhesive. Variations would include how much flap or seam overlap, etc.
Rats, my too-clever URL is knackered. Any chance you can fix my screwup?
“I think what I’ve discovered is a tin foil hat won’t work because of the large hole you need in order to stick your head into the hat. You need a tinfoil jumpsuit of some sort. I’m not sure how you can make provisions for eyeholes.”
Lucia, did you say that with a straight face? It is probably from heat exhaustion but that image you painted has me into a fitful laugh.
I don’t think a truly paranoid individual will ever feel completely safe. Those telepathic people DeWitt describes are scary.
Re: Kenneth Fritsch (Jul 19 13:13),
That’s what the lead character in the series thinks until she actually experiences the gestalt, which could be achieved by a non-telepath through physical contact with one of the telepaths. Look at it from the other side. Imagine how stressful it would be for a telepath to read the thoughts of non-telepaths with all their hidden guilt, hates and fears. Fortunately, physical contact is required and the telepaths live in what amounts to a gated community with only a select few making occasional contact with non-telepaths, generally to resolve criminal investigations.
Lucia,
Attenuation sufficient to keep your phone from ringing may not be sufficient when you are close to a cell tower. Really deternining what would be adequate would require testing over a range of distances from cell towers.
DeWitt Payne (Comment #117827)
July 19th, 2013 at 1:49 pm
“That’s what the lead character in the series thinks until she actually experiences the gestalt, which could be achieved by a non-telepath through physical contact with one of the telepaths.”
Not sure what kind of physical contact that might have been but if I let imagination run, I would suspect there would be no need for talking during it. Faking it would not work either.
Kenneth
Was the initial discussion said with no grin? 🙂
SteveF
Agreed. I’ll try to discover where the nearest tower is. But I know that if it rings, the thing is not working.
Earl–
Whatever url was inserted, it’s gone. Just paste it in.
As for sewing: Whether I am deft or not, the needle does poke small holes. But I think that doesn’t make the difference because folding over fixed the issue (provided I hold carefully.) The problem is the way I constructed was to just place the two slabs of insulated fabric with the foil sides facing, then I took bias tape on the outside of those and sewed through. I did it this way to reduce bulk in the seams.
The more conventional constructions for clothing would be to place the fabric with the blue-non-foil sides together, stitch, then turn inside out. Then you have bulk on the inside. But that seems to be a good thing in this instance!
So the foil is not folded there. I think the thread doesn’t press the foil – to- foil well enough.
I am going to have to drive out near the tower and do some tests though. Right now, I have two different sacks. The “sack in a sack” definitely works in my kitchen. But if one is worried about being tracked, they don’t want to suddenly be trackable when they decide to shop at ALDI’s!
My URL was just linking to 3M magic tape. Nothing productive, just smartassery. My point about prototypes is that if it were me, I’d do the mockups using tape to hold things together rather than sewing. You likely can sew much more efficiently than I so it may be irrelevant.
Anyhoo, I love the empirical nature of this project. I’m now wondering how one might measure the cell signal strength with a smartphone.
Lucia,
Are you by chance testing with an Android smartphone? There is an app on Google Play called Cell Logger 2 that will monitor the signal strength of the current cell tower and log any changes in signal strength. I just installed it on my Samsung Infuse and it does exactly that. I tried it out and found that putting the phone in a skillet with lid knocks the signal down by about 15 dB but does not kill it. Probably due to poor fit on the skillet lid. Now I need to see how I can kill the signal, preferably without using up half a meter of aluminum foil.
Earl–
I have a sewing machine. Stitching is easy.
I don’t have an Android smart phone. But whether or not I can measure the tower strength, I figure being fairly close will maximize. The only thing is I need to cell phones to do the test near the tower. (I have access to two– but Jim’s is generally with him.)
On tracking: I figure that we don’t need to kill to avoid tracking. You just need to attenuate enough to prevent the tower from detecting. Of course, I could be wrong!
I think the lid does need to fit very well. The all clad lids have a sort of “dip” which may help. But placing the el-cheapo pie plate over didn’t work. And the thickness of that plate is much larger than the foil, so I suspect it was the poor seal.
I can report replication of your methodology. I fetched the snug-fitting lid from the dishwasher and tested with that. Tada, calling the phone yielded no connection. After pulling the phone out of the skillet it showed it was re-establishing cell tower connection.
Cell Logger 2 (CL) logged a signal strength of -113 dbm*, whereas it’s about -85 to -91 dbm in my kitchen. The earlier poor-fitting lid experiment resulted in an attenuation to -107 dbm. According to these guys, the signal drops at -112 dbm.
http://www.tested.com/tech/android/557-how-to-measure-cell-signal-strength-on-android-phones/
So if you’re thinking of field testing your prototype before going to full production, this is a tool that could be useful. Also for anyone crafting their own Snowden Sack and wondering if it is effective.
* The dbm unit as displayed on the phone screen. Per Wikipedia “dBm (sometimes dBmW) is an abbreviation for the power ratio in decibels (dB) of the measured power referenced to one milliwatt (mW)”
Lucia, aluminium does not easily form good electrical contact due to the surface oxide layer. Craft shops and others sell copper based foils that may help.
It’ll cost more but, in my opinion, will look rather more stylish and fashion-conscious in the high street.
Brandon was blocked but sent me his comment:
Earl
Full production is (a) make one for me, (b) send one to Roger and (c) give a few to friends! There are some that are supposedly commercially available. I don’t know how well they work– but making a real one to sell would require figuring out a model that one would get sweat shop workers to make!
But if Brandon is right I need to test actual attenuation so I can know that it’s really untrackable. After all: Roger removes his battery. Clearly, he wants to be sure it’s untrackable.
Lucia,
Sorry, should have used the /deadpan tag when referring to your full production. 😉
Brandon’s concerns seem valid to me. Right now you know that your sack is a “Don’t bug me” bag. You know you can’t receive calls on your phone but you don’t know to what extent the cell towers can connect to the phone. It would be useful in the pursuit of knowledge to be able to quantify how effective a given design is in attenuating / damping / blocking the radio communication between phone and tower.
As far as GPS goes, my experience is that GPS demands a near clear-sky view in order to get anything remotely accurate. I have no confidence that just because I tell my phone not to turn on the GPS receiver that it’s beyond the capabilities of a clever three-letter agency (TLA) to turn it on remotely. So cloaking the phone in a SnS (Snowden Sack, but avoiding the SS abreviation) will prevent getting a lock on the GPS satellites. So if one is worried that their phone is acting like an ankle bracelet, putting it in a SnS will disable that feature.
But the potential for the phone to intermittently connect with a cell tower means that the TLA could locate your phone to say, a given part of town. If the phone connects with many towers at once then triangulation would allow for somewhat accurate location, at least for the purposes of pinning the phone down to a specific neighborhgood at a precise time. To have full confidence that the phone is not being tracked while powered up, you’d want to know just how well the SnS is blocking that signal.
Lucia,
The bag has to be one conductor. The entire cage has to be electrically bonded together. Multiple sheets of foil are not typically bonded together. Measure the resistance : ) Aluminum and any thin sheets of oxidizing metal are not ideal.
For testing, make a ‘directional’ version like a tube that you can see into and observe the bars.
Try it with copper sheeting and you will notice a huge difference.
Would the sack be effective against “stingray” phone trackers?
Kusigrosz —
Well… I had to look up “stingray” phone tracker. But it seems to me that if the bag works it should be effective because the sack should make the phone invisible to the tower and the stingray tower is simulating a cell phone tower. It’s just that the stingray is ‘faking’ it and can move around on a vehicle or something.
I should note that if someone is actually following you around tracking, you are going to get monitored (a) should you use the phone and (b) possibly visually when you aren’t using the phone. So you need more than a sack!
Firstly you’ve made a huge mistake by discussing your plans on a public forum. There’s probably already a boffin designing an anti-sack.
Secondly if you’re doing nefarious things wouldn’t it be easier just to leave your phone behind. Switched on, sitting on your favorite TV-watching armchair should fool the spooks. There’s nothing more embarrassing than your phone going off when you’re sneaking behind UEA-CRU security guards and I hear Big Oil hates having his clandestine meetings interrupted by the Nokia ringtone.
HR,
Of course it’s easiest to leave a phone at home. But if I’m doing nefarious things I might have a sudden need to communicate (at my discretion.)
Clearly those doing nefarious things need to have their “home” phone everyone knows they own and also some sort of set of disposable phones (which they carry around in Snowden Sacks, then use when needed, and likely, dispose of after a day or two.) Of course this could all get pricey.
Honestly, I’m not sure why people in crime dramas don’t carry two phones. I saw a Swedish crime drama and the mole in the police office who’d been sending info to the criminals was ultimately caught when an officer got the main criminals phone and auto-dialed her phone, which was sitting on her desk in the police office. Why didn’t she have a main phone (sitting on the desk) and a super-secret other phone set to silent buzz or voice answer so she could just get messages? Oh well. I’d attribute it to just being fiction, but I bet her owning only one phone is probably no less unrealistic than the rest of the plot points.
lucia:
Because real life the criminals that you’d hear about and they’d make a movie of would do dumb things. Aaron Hernandez’s apparent involvement in the murder of Odin Lloyd is an example of that. Forget catching a person at a location via their cell phone pings (they did that too), Hernandez left a nice trail of text messages between him and Lloyd on the night of Lloyd’s murder.
“Honestly, I’m not sure why people in crime dramas don’t carry two phones. I saw a Swedish crime drama and the mole in the police office who’d been sending info to the criminals was ultimately caught when an officer got the main criminals phone and auto-dialed her phone, which was sitting on her desk in the police office.
Lucia, sounds like you watch foreign mysteries with sub titles on MHz. I am hooked on watching at 8:00 PM. Maigret is my favorite. Detective Salvo Montalbano is a good mix of comedy and mystery although his forever missing connections with his girl friend, Livia, gets pretty predictable. I like Annika Bengtzon and Irene Huss as a change of pace but they include too much of their domestic problems.
Lucia, that lady mole was an office worker and not a detective. She was not trained for intelligence work and cried like a baby when she was caught. I think the writers were trying to show that she was under the influence of the evil bad guy just like the witnesses were. I thought for a moment the chief detective was going to answer it.
Kenneth
Me too!! As you live near me, I’m sure it’s the same show on the same channel!
We haven’t watched the other ones yet. We just got hooked on the rotating shows recently.
Me too.
Yes. She was an office worker. But still. You’d think if you worked with police often enough you’d pick up some sort of procedure. (There must be some… right?). Like:
“Rule 157: When being a mole for criminals, get a throw away phone ‘just for them’. ” In fact, given how organized the criminal involved seemed to be, you’d think he would advise such a thing as her being fingered does potentially create one more ‘witness for the prosecution’. But. No. There he has her regular ol’ cell phone number programmed into his cell phone auto-dial.
Still: as I said, I suspect this was no more unrealistic than a number of other things in the fictional crime drama.
I miss Beck, particularly following Gunvald.
One of my favorite massive plot holes along this line was in the TV series Alias, where supposedly the CIA internal network was on Wi-Fi! Worse, it got hacked by a tiny brooch that could somehow magically re-transmit the signal to a receiver miles away. If the walls were really that porous, a directional antenna would have worked.
Then there are the magical analytical instruments on the various incarnations of CSI, not to mention physicians performing their own clinical lab tests on House. There’s even a CSI effect.
Martin Beck is probably worth watching for the conversations and drinks he has at the end of the day with his neighbor, but his show, like the other Swedish mystery shows at MHz, get way too involved for my tastes in their family problems -which always seem related to work causing the neglect of other family members. As a libertarian and a civil libertarian I must say that, while Gunvald uses his government endowed power too freely, I have to admire his ability to think for himself and get a job done. He makes Beck seem like a mincing bureaucrat.
Lucia
I don’t think the criminals have learnt how to seal the phone. see
Criminal caught by iphone he stole
Better to wrap the thing in fine mesh copper screening (more available than copper foil, although you can buy the foil at McMaster) or in one of those silvery conductive bags they ship electronics in.
Snowdon Sack
Lucia
I have a belt container for a mobile phone bought from a store. It has separate pockets for the phone and a battery – from the phone or spare. It it is made of compressed card covered in fabric and with a plastic zip. It completely shields the phone from incoming calls though I have not been able to measure wether or not any emissions from the phone, if switched on, are detectable.
Re: Eli Rabett (Jul 26 00:28),
Tried it. Doesn’t work. Those bags are for static charge, not RF. The conductivity isn’t very good, orders of magnitude lower than Al or Cu.
I wonder what the in-bag battery life is, and also what the temperature inside the bag will rise to. Cell phones work harder in lo-signal areas and inside the (Faraday shield) bag is about as low as a signal gets. It also happens to be a decent heat shield. The greater concern is a battery fire from excess heat.
When I travel I put my iPhone in “Airplane mode” as it is prone to attaching to Canadian towers (I’m in the US) where expenses are greater. BT is always off, and location services likewise.
err, turn your phone to airplane mode
http://www.youtube.com/watch?v=tw9vEiys2Zk
lots of youtubes