It all stemmed from a number of unexplained, seemingly spontaneous, fuel fires at service stations and wireless transmitting devices were very strong suspects as the cause of it hence laws/rules were implemented in the interests of public safety. Those rules have never been relaxed but some study of security videos that captured these spontaneous fires revealed that the real culprit was static electricity discharges when people got into, and out of, the car while refuelling was in progress IE cloud of highly flammable vapour + spark = bang and flames. It was more likely to happen when the fuel nozzle was the 'latching' type that could be left filling (with auto stop) while the driver went rummaging in the car for wallet/phone etc. I haven't seen such a nozzle for a long time now, they all have to be held throughout the process presumably as a safety measure to reduce the possibility of the operator accumulating a static charge in relation to the car body while fuel was flowing.
It's never been conclusively proven that a small transmitter could not produce such a spark so the rules will stay. It's all about public liability and the cost of insuring against it.
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