How NFC technology actually works
NFC is a radio technology that only works over a very short distance. The surprising part is that passive tags have no battery: the magnetic field produced by the reading phone also supplies the power that wakes the chip inside the card.
The field carries the power, the data rides on it
The phone generates a field at 13.56 MHz. The antenna inside the tag harvests energy from that field by induction, the chip wakes up and sends back whatever it stores. That's why an NFC sticker still works after years in a drawer — there's no battery inside to run flat.
NDEF: the shared data language
For phones to understand each other, the data needs a common format, and that format is NDEF. An NDEF record can carry text, a URL or a MIME type. For a business card, the typical payload is a contact record with the `text/vcard` type; when the phone sees it, it offers to save the contact directly.
HCE: the phone impersonating a card
Host Card Emulation lets a phone behave as if it were an NFC tag. The app answers the reader in the background and the same data moves across with no physical card involved. That's exactly what Business Card Tap does: it presents the phone as a Type 4 tag and delivers the vCard. (This is an Android capability; Apple doesn't open this kind of card emulation to third-party apps.)
Frequently asked questions
How is NFC different from Bluetooth?
NFC needs no pairing and is limited to centimetres; Bluetooth has long range but requires a connection step. NFC is sometimes used just to kick off a Bluetooth pairing.
How much data fits on an NFC tag?
Common tags hold anywhere from 144 bytes to a few kilobytes. That's usually enough for a contact record; for anything long, writing a link is the safer choice.
Does it work while the phone is locked?
On the reading side, most phones need the screen on. For card emulation the behaviour varies by device, but generally the screen must be on and the phone unlocked.
Turn your phone into your business card. Business Card Tap sends your details to another phone with a tap over NFC, and falls back to an on-screen QR code when NFC isn't available. Fully offline, no account.
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