How do contactless cards work?

The original aircraft-tracking technology has evolved to change the way we pay

In the UK, when you tap your contactless card you can spend up to £30 in the space of a second. Some people love it, some people are unnerved by it, but have you ever left the till wondering how it can be so straightforward?

These payments use technology called radio frequency identification (RFID). Today there is rising demand for this equipment, with contactless payment being the most common method for in-store card transactions. RFID enables encoded digital data to be transferred via radio waves between two devices. In the case of contactless payment, data is provided between a card and card reader. While they need to be in close proximity to establish a connection, they do not need to come into contact. This form of RFID, used in transmitting data over short distances, is called near-field communication (NFC). NFC technology has gone a step further in speedier payments by enabling people to pay contactlessly using a smartphone.

The recent developments have definitely drawn more awareness to RFID, but when did it first come about? This seemingly modern technology actually emerged before World War II. Sir Robert Watson-Watt is believed to be the first to use radio to obtain data in this manner when he discovered a way to source information about aircraft. His system, radar, was able to detect and reveal limited data about planes, such as its size and whether an aircraft was friend or foe.

The next major progression for RFID was creating affordable commercial applications. Security tags for shops followed, with a simplified early system that only required shopkeepers to switch tags between their two states so that they didn’t trigger the door alarm.

In 1973, a more complex version was created; an active tag with rewritable memory. Further advancements in RFID have seen a variety of applications, from tracking transportation of nuclear materials to identifying individual cows for agricultural purposes, come into widespread use.

The science behind the tap


An intricate design

Built into contactless cards is a small microchip containing account information. A connected copper wire increases the area for detecting signals.


Two-way connection

Card readers emit radio waves. When a card is placed close enough, the reader is able to send transaction details. The card’s microchip returns a signal, responding with payment details so the transaction can be processed.


Top secret coding

The communication takes place using an encrypted language to avoid cloning.

Avoiding contactless crooks

It can be easy to get lost in the convenience of a contactless lifestyle, forgetting the potential dangers. While it has become easier for you to pay, this new method means that thieves can pickpocket digitally. Using an app that costs just £5 and has been downloaded 1 million times, people can gather the credit card details of anyone within range. This method of stealing data using RFID is called ‘skimming’.

However, there are now precautions you can take to enjoy the perks of contactless while keeping your details safe. Wallets like the ‘Ekster’ wallet are designed to block transmissions, as they encase your cards in a protective aluminium card holder. These work because radio waves cannot travel through all materials. The thin metal layer prevents signals travelling in either direction.

This article was originally published in How It Works issue 129, written by Ailsa Harvey 

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