Where the antenna is, and what the settings allow

Two things only the device can answer: where its NFC antenna physically sits, and whether NFC is restricted to an unlocked screen.

Both of these describe the hardware in the user’s hand rather than anything your app does with it. They exist because the two most common complaints about an NFC screen — “it never reads” and “nothing happens on the lock screen” — usually have nothing to do with the tag.

Where to tell the user to tap

Android 14 added an API that reports where the NFC antenna physically sits on the device. It is the difference between a card illustration in the middle of the screen and one over the antenna.

import { nfc } from 'react-native-nfc-kit';

const info = await nfc.getAntennaInfo();

if (info !== null) {
  const [antenna] = info.antennas;
  // Millimetres from the bottom-left corner of the device.
  console.log(antenna.locationX, antenna.locationY);
}

The coordinates are millimetres from the bottom-left corner of the device — the corner of the hardware, bezels included. They are not screen coordinates and not pixels, so they mean nothing on their own. That is why deviceWidth and deviceHeight come back in the same object: it is the ratio of the two that becomes a position you can lay out against.

import { nfc } from 'react-native-nfc-kit';

const info = await nfc.getAntennaInfo();
const antenna = info?.antennas[0];

const hint =
  info === null || antenna === undefined
    ? null
    : {
        left: `${(antenna.locationX / info.deviceWidth) * 100}%`,
        // Measured up from the bottom, which is the opposite of a CSS `top`.
        bottom: `${(antenna.locationY / info.deviceHeight) * 100}%`,
      };

A phone can report more than one antenna, and antennas is ordered as the platform gives it, with no promise about which is the “main” one. Most devices report exactly one.

When it is null

null is a normal answer, not a failure, and it covers four different situations on purpose:

Situation	Why
iOS	CoreNFC never reports antenna geometry, at any iOS version.
Web	A page is handed records, never anything about the radio.
Android 13 and earlier	The API arrived in Android 14 (API 34).
Android 14 where the OEM left it empty	Common. The numbers are the manufacturer’s to fill in.

The last row is the one worth designing around: it means the null branch is not “the iOS branch” by another name, and a device on the right Android version can still decline to answer. Keep the generic illustration as the fallback.

Because of that, getAntennaInfo() resolves null rather than rejecting — a screen laying out a hint needs no try/catch. If you want the answer without the round trip, nfc.capabilities?.antennaInfo is the same fact as a boolean.

On a foldable, deviceFoldable is true and every number describes the device unfolded. A folded phone needs its own arithmetic before any of this reaches a layout, and the platform gives you nothing to do it with — so on a foldable, showing the generic hint is usually the better answer.

Secure NFC

Android 10 added a setting called Secure NFC: when it is on, the device reads tags only while the screen is unlocked. It is off by default on most devices and on by default on a few, and a user can turn it on without connecting it to anything.

import { nfc } from 'react-native-nfc-kit';

if (await nfc.isSecureNfcEnabled()) {
  // A tap on the lock screen will do nothing at all. Say so, rather than
  // letting the scan sit there looking broken.
}

This is a call rather than a capability because the user can change it from the settings while your app is running. Whether the device has the setting at all is nfc.capabilities?.secureNfc, which is false below Android 10, on iOS and on the web — and isSecureNfcEnabled() is false there too.

It matters most for background and launch tags: a tap against a locked phone is exactly what that feature is for, and Secure NFC is the reason it silently does nothing on some devices. A reading session started from a screen the user is looking at is unaffected, because the screen is unlocked by definition.

What each platform reports

	iOS	Android	Web (Chrome)
getAntennaInfo()	null	API 34+, and only when the OEM filled it in	null
isSecureNfcEnabled()	false	API 29+	false

Neither call needs a permission, an entitlement, or anything in the manifest. Both are safe to call on every platform on startup.