Before modern plastic debit cards with magnetic stripes, the world's first automated teller machine in 1967 relied on a surprising security mechanism: radiation. Installed by Barclays in London, the machine required customers to insert special paper vouchers purchased from a teller. To prevent fraud, the vouchers were impregnated with carbon-14, a mildly radioactive isotope. The machine detected the radiation signature to verify and process the withdrawal.
The 1960s Banking Bottleneck
In the mid-twentieth century, withdrawing cash was strictly tied to branch operating hours. Commercial banks closed their doors in the early afternoon on weekdays and remained shut over the weekend. For workers earning weekly wages or individuals needing funds outside standard business hours, there was no alternative way to access money held in their accounts. Cashing a cheque required standing in line during business hours or relying on local shopkeepers willing to accept personal paper cheques.
As consumer commerce expanded throughout the 1960s, financial institutions recognized that physical branch counters were becoming an expensive operational bottleneck. Banks sought mechanical methods to automate routine transactions, specifically the distribution of physical banknotes. The core engineering challenge was not merely dispensing paper money, but doing so securely without a human teller present to verify the identity of the customer, evaluate account balances, and protect against counterfeit instruments.
The Enfield Installation and Carbon-14 Vouchers
On 27 June 1967, Barclays opened the first automated cash dispenser at its branch in Enfield Town in north London. Developed by an engineering team led by John Shepherd-Barron at De La Rue Instruments, the machine—known as the De La Rue Automatic Cash System, or DACS—introduced self-service cash dispensing to the public. Actor Reg Varney was invited to make the ceremonial first withdrawal, demonstrating the capability to the press.
Because modern magnetic stripe cards and networked computers did not yet exist in consumer banking, the machine could not read electronic data or query a central database. Instead, it operated entirely offline using specialized paper cheques or vouchers purchased in advance from bank tellers. To prevent customers from using photocopies or forged documents, De La Rue impregnated the paper vouchers with trace amounts of carbon-14, a mildly radioactive isotope.
When a customer fed the voucher into the machine's intake slot, internal sensors measured the distinct radioactive emission profile of the carbon-14. This radiation signature served as a physical cryptographic watermark. If the machine detected the correct isotopic signature, it recognized the voucher as genuine and proceeded to verify the user's identity.
Offline Authentication and the Four-Digit PIN
Detecting a genuine radioactive voucher was only half of the security equation. The dispenser also needed to confirm that the person presenting the voucher was its rightful owner. To accomplish this, the De La Rue system implemented a personal identification number (PIN) system, matching numbers entered on a physical keypad against the data encoded on the physical voucher.
Shepherd-Barron originally intended to use a six-digit numerical code, drawing inspiration from military identification numbers he had memorized. However, after discussing the concept with his wife, Caroline, he discovered that she found six consecutive digits difficult to recall consistently, preferring four. The team adopted four digits, establishing a standard for personal authentication numbers that persists across global banking systems today.
Because the machine was an offline terminal, it retained each used voucher after dispensing the cash. Customers were limited to a fixed withdrawal amount—typically ten pounds per transaction—per voucher. The bank gathered the deposited paper vouchers from the machine at a later time and manually debited the corresponding customer accounts, treating the vouchers much like processed paper cheques.
Parallel Inventions and the Race to Automate Cash
The Barclays installation in Enfield was not the only effort to mechanize cash dispensing during the late 1960s. Several competing teams across Europe, North America, and Japan were developing independent devices using distinct authentication mechanisms. In the United Kingdom, Westminster Bank partnered with Smith Industries and the Chubb lock company to deploy the Chubb MD2, which utilized plastic cards with encoded outer punches rather than radioactive paper.
In the United States, engineers at Docutel developed the Docuteller, deployed by Chemical Bank in New York in 1969, which read reusable plastic cards with magnetic stripes to authorize transactions. Meanwhile, in Japan, early automated cash devices were being engineered to read specialized magnetic tokens. Each design grappled with the same fundamental constraint: verifying customer identity and instrument validity without access to a real-time communications network.
The Shift to Magnetic Stripes and Live Networks
The era of radioactive paper vouchers was relatively brief. Single-use vouchers presented major logistical challenges, as customers had to visit a branch during business hours to purchase the vouchers in the first place, partially undermining the convenience of self-service. Furthermore, retaining and manually sorting thousands of paper slips imposed significant administrative overhead on bank branches.
By the early 1970s, advancements in magnetic recording technology and standardized plastics enabled the widespread adoption of reusable magnetic stripe cards. In 1972, Lloyds Bank introduced the Cashpoint machine in the UK, developed in conjunction with IBM. Unlike earlier stand-alone dispensers, these machines were connected via telecommunication lines to a central mainframe computer.
This online connectivity eliminated the need for exotic physical security measures like radioactive isotopes. Instead of relying on the material properties of paper vouchers to prevent fraud, networked ATMs could check card data, verify the PIN against central databases, check live account balances, and immediately deduct the withdrawn funds, laying the groundwork for the modern global ATM infrastructure.
Key takeaways
•The world's first automated cash dispenser was installed by Barclays in Enfield, London, on 27 June 1967, developed by De La Rue.
•Because magnetic stripes and real-time computer networks were not yet available, the machine verified single-use paper vouchers impregnated with mildly radioactive carbon-14.
•The machine paired isotopic verification with a four-digit personal identification number (PIN), establishing the four-digit standard still used globally.
•Radioactive vouchers were phased out in the early 1970s as banks transitioned to reusable magnetic stripe cards connected to real-time mainframe networks.