The first cash machine ran on radioactive vouchers

On 27 June 1967, at a Barclays branch in Enfield, north London, an unheard-of machine made its debut: you fed it a paper voucher, typed in a code, and it handed you cash. The first customer was Reg Varney, a famous British television actor — because even a cash machine needs a red carpet.

Its inventor, John Shepherd-Barron, got the idea in the bath while nursing a grudge: he had arrived at his bank a minute late and been left without cash for the weekend. If one machine could dispense chocolate bars, he reasoned, another could dispense banknotes.

Magnetic-stripe cards didn't exist yet, so the vouchers were impregnated with a trace of carbon-14, a harmless radioactive isotope the machine knew how to detect. The limit per withdrawal: ten pounds — "quite enough for a wild weekend", according to its inventor.

One detail remains that you use every week. Shepherd-Barron wanted six-digit codes, but his wife, Caroline, protested: four was all she could remember. The four-digit PIN you type today is, in fact, the memory of a lady from 1967.