What an NFC tag is.
An NFC tag is a small chip with an antenna and no battery, powered by the phone that reads it from a few centimeters away. It stores a short NDEF message, usually a web address. Tapping a phone to a tag on a business card opens that address, which is how an NFC business card opens a digital one.
Make your free cardA free Apple Wallet business card, in about a minute
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- Range
- A “typical range of up to 2cm”, says the NFC Forum.
- Tag types
- The NFC Forum defines five, which “differ by the underlying communication protocol and data structure to store NDEF messages.”
- Memory
- Small. The common NTAG213 holds 144 bytes of user memory, per NXP’s datasheet.
144 bytes is plenty for an address.
Most business card and sticker tags use NXP’s NTAG21x family, which NXP itself lists for business cards.
| Chip | User memory | Used by cardr.co/yourname (25 bytes) |
|---|---|---|
| NTAG213 | 144 bytes | 17% |
| NTAG215 | 504 bytes | 5% |
| NTAG216 | 888 bytes | 3% |
Memory from NXP’s NTAG213/215/216 data sheet, Rev. 3.2. Bytes computed below for the full NDEF message.
- A card’s address
A card’s tag, byte by byte.
This is the exact message a tag holds to open a card at cardr.co/yourname: 25 bytes, computed on this page. A tag holds no name, number or photo.
- StartNDEF follows
- Length22 bytes
- Record headerOne short record
- SizesPayload 18
- TypeU: a web address
- Prefixhttps://
- The addresscardr.co/yourname
- EndStop
What the phone has to do.
On iPhone, tags are read with no app on iPhone XS and later, which Apple calls background tag reading. Apple says it works only while the iPhone is in use, takes the first web address on the tag, and shows a notification to tap. Android phones read tags whenever NFC is switched on and the screen is unlocked. A tag that does nothing is usually the phone’s setting, the case, or the reader’s position; our guide to an NFC card not working on iPhone walks through each.
Because a tag holds only an address, rewriting it is all it takes to point an old NFC card at a new digital card. Free writer apps do this on any NFC phone.
-
iPhone XS and later
- In use
- Notification
- Page opens
-
Android
- NFC on, unlocked
- Page opens
-
When it fails
- NFC off, thick case
- Nothing
Where these facts come from.
Primary documents only: the standard, the platform’s own documentation or the chip maker’s datasheet. Each was read on October 29, 2026.
- NFC Forum: NFC Technology: five NFC Forum tag types that store NDEF messages; a “typical range of up to 2cm”
nfc-forum.org/learn/nfc-technology/Read October 29, 2026 - NXP: NTAG213/215/216 product data sheet, Rev. 3.2, June 2, 2015: NFC Forum Type 2 Tag ICs with 144, 504 and 888 bytes of user memory; business cards named as a target use
www.nxp.com/docs/en/data-sheet/NTAG213_215_216.pdfRead October 29, 2026 - Apple Developer: Adding Support for Background Tag Reading: “iPhone XS and later support background tag reading,” only while the iPhone is in use, using the first URI record on the tag
developer.apple.com/documentation/corenfc/adding-support-for-background-tag-readingRead October 29, 2026
Common questions.
What is an NFC tag used for?
Opening something with a tap: a web page, a Wi-Fi network, an app. Payments and transit cards use the same radio with secure chips; the tags on business cards and stickers are the simple, rewritable kind.
Does an NFC tag need a battery?
No. The reading phone’s field powers the chip for the moment it is read.
Can someone steal data from my NFC business card?
There is nothing private on it. A business card tag holds a web address, the same one your QR code shows, and it can only be read from about 2 cm.
Which NFC tag should I buy for a business card?
An NTAG213 holds a card address many times over. Larger chips only matter for long content, which a business card tag should not carry.
What does “NFC tag detected” mean on my phone?
Your phone’s reader found a tag nearby, often in a card, a sticker or another phone’s case, and read what it holds. It does nothing until you tap the notification.
Point your tag at a card worth opening.
Write your Cardr address to any NFC tag you own and a tap opens your card, the same page your QR opens. Free forever.