A card reader captures the card, encrypts the details on the device, and sends an authorisation request to your acquirer, which routes it through the card scheme to the customer's bank. The bank answers yes or no and the terminal prints or sends a receipt. The whole round trip usually takes about two seconds, and the money moves separately, later.
How do bank card readers work, from tap to approval
The reader captures the card by its chip, its contactless antenna or a phone wallet held against it, and encrypts the details inside its own certified hardware. It sends an authorisation request to your acquirer, which routes it through the card scheme to the customer's bank. The bank answers yes or no, and the terminal prints or sends a receipt. That round trip usually takes about two seconds. The money itself moves separately and later, when the acquirer settles the day's takings to your account, which is why an approval on screen and money in the bank are two different events.
What the reader keeps and what it never sees
Card details are encrypted in the reader itself, which is why the hardware has to be certified and why a reader from one provider will not work on another's account. Your phone or tablet runs the app and shows the total; it does not handle the card data. That separation is what lets a consumer tablet be part of a compliant setup at all.
Do card readers need internet? When the connection drops
Bluetooth readers depend on the paired phone, so a phone with no signal means no sale. Wifi terminals fail with the network. Machines with their own SIM keep working where there is mobile coverage. A few terminals support an offline mode that stores a transaction for later authorisation, which shifts the risk of a decline onto the merchant, so check whether yours does and whether you want it on.
A debit card reader takes credit and wallets on the same device
The reader does not care which it is, and that answers how do credit card readers work differently from debit ones: they do not. It reads the chip, the contactless antenna or the phone wallet and passes the same request. What differs is the cost behind the scenes, because interchange is capped lower on UK consumer debit cards than on credit cards, and commercial and overseas cards sit outside the caps entirely.
Other questions people ask
How long does a card reader take to authorise a payment?
About two seconds in normal conditions. The delay a customer notices is usually the network, not the terminal, which is why 4G machines feel faster than a Bluetooth reader on a weak phone signal.
What is a card reader used for?
Taking a card payment in person. It reads a customer's chip, contactless card or phone wallet and passes the payment to an acquirer for authorisation, while your phone, tablet or the machine's own screen shows the total and the receipt.
How do chip and pin machines work when a card is inserted?
The machine reads the card's chip, the customer enters their PIN on the machine's own keypad, and the request goes to the acquirer exactly as a tap would. A contactless payment above the ceiling is declined and the customer is asked to insert, which is why every reader here also has a PIN pad.
How do credit card machines work without a phone?
A standalone machine has its own screen, keypad and SIM or wifi connection, so it runs the whole trip itself and prints its own receipt. A Bluetooth reader does the card part and leaves the screen, the app and the connection to the paired phone.
Do card readers store card numbers?
They encrypt card data on the device and pass it to the acquirer. They are not designed to retain usable card numbers, which is part of what the hardware certification exists to guarantee.
Can a wireless card reader work anywhere?
Only where its connection works. Bluetooth readers need the paired phone to have signal; wifi terminals need a network; SIM terminals need mobile coverage. Check coverage at the places you actually trade before buying.
What does a card reader do that the acquirer does not?
The reader captures and encrypts the card inside its own certified hardware, which is why one provider's reader will not work on another's account. It does not hold your money, set your rate or settle the payment; that is the acquirer behind it. The reader is the part you can see, and the smaller part of what you are buying.
What do card readers do when the network drops?
It depends which kind you have. A Bluetooth reader depends on the paired phone, so no signal on the phone means no sale. A wifi terminal stops with the network. A machine with its own SIM keeps working anywhere there is mobile coverage, and a few terminals support an offline mode that stores the sale for later. Choose on the failure you can least afford.