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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