Got a signal problem on the weekly shop?

Got a signal problem on the weekly shop?It’s not often that I write a rambling post… well, OK.. perhaps quite a few of you would disagree with that. The thing is, I’ve noticed something. This weekend we were shopping at the local Tesco. It’s the usual scene, you put a few items in the trolley and then you wince at the bill.

Thing is, I never get a mobile signal in there. Being the geek I am, I know which transmitter my mobile is connected to (it just takes a quick look at this). In this case, it was literally 200 metres away on the local fire station. So why the heck was I not getting any mobile signal ?


Well, I’ve had a butchers around and there’s a few people thinking that supermarkets and other stores are putting signal blockers in place. However, according to what I’ve found on the Ofcom site, it’s not actually legal to use jamming devices here in the UK.

Jammers are also subject to the Electromagnetic Compatibility Directive (EMC) Directive (which specifies) that all electrical and electronic apparatus placed on the market or taken into service in the UK, including imports, satisfy specific requirements to ensure that they do not cause excessive electromagnetic interference or are adversely affected by it and have to carry the CE mark to show compliance.

Often targeted for use in such areas as theatres, cinemas, examination halls and libraries where the use of mobile phones can prove annoying, jammers are likely to affect wider areas and other frequencies than those they are intended for. They can also result in the disruption of emergency and rescue radio services in the public area.

The Ofcom guys state that alternatives should include “education” and basically telling people not to do it. So, it’s not allowed, so there’s no jammers..

..well, that’s not strictly true.

Some companies, especially those with sensitive data to protect, employ devices to detect mobile phones. These devices can detect WiFi devices too. Do they “jam” them? No, but they can tell the security guys where the devices are so they can pay you a quick ”visit”. It should help to stop important data floating out the door.

Does that explain why the mobile phone signal is so crap at your local super-mega-hyper-market-store? Not really. It’s probably more to do with the fact that you’re walking around in a massive Faraday Cage and the signals are getting bounced all over the place. Most supermarkets are big metal boxes and, with more and more buildings getting hefty insulation, those mobile signals have a tough job to do.

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  • Matt

    Our local Tesco Extra now provides free WiFi to customers; so I don’t think they are trying to stop you transmitting data.

    I think your comment about a Faraday cage is spot on though.

  • Nick

    I can barely ever get a signal in my local Morrisons – it’s been the case with both O2 and Vodafone. I always figured it was something to do with the big metal roof, didn’t realise there was a scientific term for it though :-)

  • Guess it depends on lots of factors, not just a shop being Faraday cage. My local Tesco is also approx. 200-300 meters from nearby base station and I easily get signal there, however it varies a lot depending on the area of the shop I’m walking around (never drops to zero, tough). Other thing is that base station is located on a mast standing on a free field with no buildings around it (just few trees, really), perhaps your area is a bit more dense to allow decent signal getting through to the shop? Just guessing.

    Nonetheless, no signal in the supermarket is rubbish – once you’re done walking through electronics/gadgets section you have too run through the whole shop to find your wife rather than just calling her to find out where she is.

  • Ant

    I noticed the same thing in John Lewis @ Home the other day – but then I noticed there signage offering free-wifi to compare prices with competitors as they were confident they where the best price.

    Really good piece here about it – http://www.johnlewispartnership.co.uk/media/press/y2011/press-release-21-october-2011-john-lewis-commits-to-free-wifi-in-all-its-shops.html

  • I think Dawid Lorenz is right – more so build building design than any thing else…. just look at how they are made…. generally big metal frames with stuff on the outside and lots of electrics. I can demo this at my local ASDA. One part ( where I get an OK signal but not great ) has been there for more years than I care to remember yet the new section which went up last year and as described above nada….

    Now consider all the price comparison apps you could use if you had signal and it fast becomes a pain….

  • Tivey2k

    This happens to me at my local Morrisons and the transmitter is on the roof of the store! However I’ve noticed it seems to be affected more around the freezer aisles – could they have anything to do with it?

  • Bazibaral

    Wow I have noticed that in our local supermarket the signal goes completely, not just gradually goes out of range but completely disappears and I joked about how they must use jammers! I bet it’s to stop people checking cheaper prices with barcodes or sharing deals.