Hacker News Reader

Comment by wcunning | Hacker News Reader

I've noticed, recently, that literally every major chain store I go into blocks my cell signal. I get full bars outside, perfect LTE, and about 5 ft past the glass doors, I'm suddenly cut off. Specifically, Meijer grocery stores and Home Depot are the worst offenders. Coincidentally they offer free in store WiFi to track me with, so I turn off my wifi radio on both smartphone and smartwatch before walking in the door... Note, this was not the case in the exact same physical stores a couple years ago, and they weren't closed for remodeling in the interim.

Does anyone know if this sort of Faraday cage technology for large buildings is easily available for me to install in my own home? If so, what's it called, what does it cost and where do I get it?

View on HN

FWIW, if they are intentionally (or unintentionally) blocking your cell signal with an electronic signal (And since you mentioned that they didn't remodel, this is the only way they could feasibly do it), they're breaking a very serious FCC law - https://www.fcc.gov/general/jammer-enforcement.

I know that the FCC is kind of regarded as a joke lately, but this is a law they take pretty seriously as jammers can interfere with E911 calls. It would just take one emergency that 911 couldn't respond to for the FCC to realize what was going on, and no large store is going to take those odds. It's likely something else.

That said, if you really believe that they are blocking cell signals, you should probably file a tipoff, as they could honestly be putting lives at risk (go to https://consumercomplaints.fcc.gov/hc/en-us and click "phone"). As far as I know there's no penalty if you are wrong (as long as you honestly believe there might be an active jammer in the area and you aren't abusing their system somehow), worst case you'll get a call confirming they don't use one.

Yeah, I think it's more what lgats suggested, and simply that they have a naturally impermeable building in the middle. Not even the cabinets, more the metal shelving up to the ceiling and such. I also notice that my current phone does a terrible job of falling back on the much more long distance 3G, so maybe that's part of it.

> Yeah, I think it's more what lgats suggested, and simply that they have a naturally impermeable building in the middle.

That kind of contradicts the OP... since they said that it was only recently that the signal stopped working, and that the building was not being remodeled during that time. So if the building is now impenetrable then something changed. Maybe modern phones just have a horrible time falling back from LTE to 4G/3G.. But if that’s the case then I feel like the OP would have checked for that since he seems to have already been tracking his connection strength over different locations and over time.

I was the OP...

I noticed this recently, but cell towers get upgraded/replaced at intervals unrelated to "nationwide rollout of LTE!" from carriers.

Why you contradict yo self...

A spectrum analyzer or SDR dongle would tip you off really quickly if there’s active jamming, and the FCC doesn’t play games with those types of violations.

I believe you can achieve the same result in your home by adding a sheet metal roof, metal cabinets, and refrigerators along every wall.

It's a rather unfortunate coincidence, isn't it? Certainly it's not their fault that their buildings just happen to be constructed in such a way, and their products arranged such that it blocks signal causing customers to not be able to compare prices and have to use their approved internet connection. /s

I see this in the Targets in my town. I just expect signal to drop to zero.

My Lowe's and Home Depot both have free Wifi. I use it all the time to use their app or site to find the location of items in store (obv. can't talk to humans).

Target (specifically mentioned by the parent) in my town also offers free WiFi.

Good luck with that. I tried unsuccessfully, to buy an item at both Lowes and Home Depot but nobody was able to determine where in the store the item was even when I pulled the information up on my phone.

Both the Lowe’s and Home Depot by me have the aisle/bay listed on their website. It’s usually super convenient, except for their numbering of end caps. That time it took a couple of tries until I found an employee who knew what was meant.

One of the Home Depot's in my area had broken Wifi for multiple months. You could connect, and go through the disclaimer, but nothing was reachable through it. Particularly annoying because the other store, which is about the same distance away, has working Wifi but horrible reception. Since I'm occasionally in each, I had to remember to forget the Home Depot Wifi and add it back in depending on when I wen tto different stores.

I would be very surprised if the benefits from blocking signal outweighs the cost of constructing the building to intentionally block signal, and the risk of being sued for it. It's probably just something that happens naturally with those types of buildings.

I have a tin roof, metal front porch and a large metal rear-facing verandah at my house.. This effectively becomes a massive faraday cage as far as my phones concerned. The things that you wish you'd considered in hindsight when choosing construction materials.

That's probably it. Perhaps I want some decorative brushed aluminum sheet metal instead of drywall...

Tin foil with a good earthing should do the trick.

Aluminum siding works pretty well!

> and refrigerators along every wall.

Seems like a sound investment!

Don't forget to stack large quantities of tin and aluminum cans about 8 feet high or so.

In terms of passive signal blocking, I wonder if the chickenwire mesh that holds exterior stucco in place could serve as an effective Faraday cage? Or aluminum siding? I'm sure the metal roof and walls of a modular storage building would.

Most businesses use metal studs to support interior walls, though I doubt their ~2 foot spacing would block wifi or cellular RF.

In terms of active cellular jamming, that should be pretty easy to detect -- by standing in an outside doorway where you'd be exposed to inside AND outside signals, and then checking if your cellular bars fade out. That should indicate that you've been exposed to an internal jamming signal, since the external signal should still remain.

It's hard to imagine that the advantage to a corporation of isolating the customer's phone would be worth the risk of FCC prosecution.

Your idea of mesh inside the stucco is way better than my idea of simply wrapping chicken wire all over the outside. Ha.

It should work, as long as it all has electrical continuity and is grounded. I think that's where a lot of normal mesh in stucco or plaster falls short; nobody is going to bother to connect it all up with copper strips or whatever if that's not their explicit goal.

Even if it's not, it should attenuate radio waves somewhat. Just not as a full-coverage Faraday cage.

> I wonder if the chickenwire mesh that holds exterior stucco in place could serve as an effective Faraday cage?

I can confirm that. I've had a shed in the past where I've used chicken wire to secure insulation and it seems to work well, albeit unintentionally at the time.

Steel roof trusses, steel roof material, and racks and racks of steel shelving don't exactly make for an ideal radio signal environment. They aren't blocking signal, you are standing in an un-intentional Faraday cage. It likely has more to do with who your carrier is and what frequency your phone is connecting at. And FWIW, you don't have to be connected to a store's WiFi for them to track you - https://www.fastsensor.us/en/ is only just one of the many companies who don't require your cooperation to track you in-store.

A common cause for this is foil backed insulation. A number of companies install this in the ceiling spaces and outside walls to reduce the energy costs of keeping the store at a comfortable level.

Could it be that they had repeater antennas before, but after the LTE upgrades, they either declined to renew the repeater leases in favor of wifi+tracking or perhaps the carriers didn't want to pay for hosting repeaters?

Or a previously good cell radio nearby was moved, decommissioned, broke down, blocked by something else.

I've noticed this, but my thought is that it is just the natural faraday cage created by having a cement building filled with metal shelves. Combine that with towers transitioning to use LTE over 3G and you get reduced coverage indoors in large buildings.

Although where I live, the introduction of LTE on low bands reclaimed from analog TV has actually dramatically increased indoor coverage

If you could publish evidence of this phenomenon, the public would be very interested.

Anecdotally, I've had the same experience. Been going to Home Depot for a number of years, routinely using the app to locate the aisle I want in the store. Starting less than a year ago my signal becomes almost unusably weak as soon as I walk through the doors. No construction on the store, same store as has been there for a decade, but something changed. Might be a coincidence.

It's somewhat similar, but AT&T (and Apple) have forced my iPhone to always join the "attwifi" public wireless networks (present in Home Depot, airports, etc.).

I can't make my iPhone NOT auto-join it, no matter how many steps, guides, hop-on-one-foot voodoo that I've tried.

The wireless network is terrible at everything except signal strength.

Buy an iPhone, and get a seperate sim card for it. That way the phone is yours. And if you are careful, it shouldn't cost you more than a 1-digit sum, and even that would only be to cover postage when you hunt down a cheap offer.

This isn’t something AT&T can force, afaik.

Two things:

1. Go to Settings > WiFi and turn Ask to Join Networks ON.

2. Any time you are auto-connected to a network and don’t want to do that again, go to Settings > WiFi, tap the blue info icon next to the currently active wifi network, and then tap Forget this Network when the details show up.

Ask to Join Networks is usually off by default. That means your phone will always attempt to join any public wifi without asking you first. Apple thinks this is friendlier for people. All known networks, once joined, will forever be auto rejoined in the future unless you turn Ask ON and forget each network you connect to (except those you trust and want to auto-join).

Thank you (for those who don’t know) but I’ve already done that multiple times. I’ve reset network settings. I’ve done crazy voodoo with restarts, airplane mode, etc.

It’s possible that it’s been “fixed” in subsequent iOS updates. I haven’t tried recently.

Do you have a Mac or iPad that it might be pulling the settings off of?

Having discussed this with a couple of friends off of here, I should add some evidence of the tracking[0]. I agree with lgats sibling comment that this is likely just a function of the construction of the building and not outright illegal jamming.

[0] https://www.walkbase.com/blog/wi-fi-analytics-in-retail-stor...

I haven't noticed it myself. Cell phone still works inside my local home depot.

Back in college the engineering building used metal plates as the outside facade, combined with concrete construction. It had a side effect of getting rid of any cell phone reception as a result, unless you were beside a window. The building was built before 2G cell phone service was a thing, so it wasn't an intentional thing.

Go to hardware store (Home Depot would be ok but watch for poor cell reception). Buy 100 rolls of chicken wire and several gross of outdoor cable clips. Tack up all over outside surface of your house.

I always assumed stores were blocking cell signal (or certainly not doing anything to improve it, like installing LTE repeaters), to prevent you from going on Amazon and finding cheaper alternatives.

"Available for me". Are you assuming we know who you are? What's available for you might be very out of reach to others. Farady cages are not some wallpaper you put on your house.

You could wrap your house in chicken wire and ground it. I think that's about as cheap and easy as it can get. Might make the HOA mad, though.

That's why you avoid you should avoid living in an area with an HOA that's made up of bored retired middle managers.

classic hackernews

Reply on news.ycombinator.com