There are three different jobs here and they are not interchangeable, which is the thing nobody tells you before the first purchase. Talking to a card yourself is the easy one and almost any reader does it. Watching a genuine terminal talk to a genuine card without disturbing either is a different problem and needs different hardware. Sitting in the middle and changing bytes as they pass is a third.
| Device | Good for | Will not do |
|---|---|---|
| ACR122U | Sending APDUs to a contactless card from a laptop. Cheap, everywhere, works with PC/SC and libnfc. | Sniffing. It is a reader, not a listener — it cannot watch someone else's transaction. |
| PN532 breakout | The same job as the ACR122U with direct access to the chip's own command set, and it can emulate a target. | Being convenient. You choose the bus, wire it, and configure libnfc yourself. |
| Proxmark3 | Sniffing a live exchange, and low-level control of the radio layer. The tool when you need to see what actually crossed the air. | Being cheap or beginner-friendly. Client and firmware versions must match exactly. |
| Contact reader (PC/SC) | Chip-and-PIN cards over the contact interface. Often the clearest way to see a full EMV flow. | Anything contactless. |