There’s a warning spreading virally on Facebook telling you to use your phone as a Bluetooth detector whenever you go to a gas station to buy fuel.
The idea is that this will reliably warn you if there are any credit card skimmers nearby, and thus protect you from credit card fraud.
But is it true? Can your phone reliably detect card skimmers using Bluetooth alone?
(Watch directly on YouTube if the video won’t play here.)
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Pingu
Presumably no one believes any more the signs still seen at some (UK) petrol stations say “turn off mobile phones” (because of fears about the combination of electomagnetic radiation from phones and petrol vapour?!
Paul Ducklin
One theory I heard giving a vaguely plausible reason for this “rule” had nothing to do with electromagnetic radiation but with the fact that old-school phones often had detachable batteries that tended to pop off if the phone was dropped, potentially (pun in10ded!) causing a DC spark at the contacts, down on the ground where petrol vapour might have collected. Presuambly hobnailed boots should be removed for a similar reason before exiting your vehicle…
David Pottage
That theory sounds plausible, though if it where the case, it would make more sense to ask patrons not to use their phones, and to leave them in the car while at the filling station, as you are just as likey to get the spark from a dropped phone if it is on or off, and asking someone to turn off their phone will increase the chance that it gets dropped as they might not otherwise handle it.
Philip Le Riche
I believe the actual reason is that if your mobile phone starts transmitting while you’re filling (presumably even just a “hello, I’m still here” to the nearest cell tower) then it may emit several watts of RF energy. The petrol pump nozzle, which may only be a foot away, would act as a receiving aerial and could cause a spark as it touches and is withdrawn from another piece of metal, such as your car. It was through observing just such a spark that Heinrich Hertz first proved the existence of electromagnetic waves, already predicted theoretically by James Clerk Maxwell.
When I first got a mobile phone I used to turn it off when I was filling up, but I think that habit lapsed quite quickly and I don’t remember ever seeing anyone else do so. And I don’t remember ever hearing a report of a fire started in this way.
Philip Le Riche
Asked about the possible applications of his discovery of electromagnetic waves, Hertz replied “Nothing, I guess”. He hadn’t though of setting fire to petrol stations since there weren’t any in those days.