> ## Documentation Index
> Fetch the complete documentation index at: https://docs.mentraglass.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Heading

> The phone's compass heading, as a continuous stream of degrees.

`session.heading` reports the phone's compass heading. Subscribe with
`onUpdate()` to get a `HeadingData` every time the heading changes.

```typescript src/background/index.ts theme={null}
const off = session.heading.onUpdate((data) => {
  session.display.render([{type: "text", id: "msg", box: {x: 0, y: 0, w: 576, h: 288}, text: `${Math.round(data.degrees)}°`}]);
});
```

Heading needs the `LOCATION` permission in your
[manifest](/app-devs/core-concepts/miniapp-manifest), the same key
[`session.location`](/app-devs/core-concepts/location) uses.

## Continuous updates

`onUpdate()` delivers a `HeadingData` on each heading change. It returns an
unsubscribe function.

```typescript theme={null}
const off = session.heading.onUpdate((data) => {
  session.display.render([{type: "text", id: "msg", box: {x: 0, y: 0, w: 576, h: 288}, text: `${Math.round(data.degrees)}°`}]);
});

off(); // stop receiving updates
```

## HeadingData

| Field     | Type     | Notes                                                 |
| --------- | -------- | ----------------------------------------------------- |
| `degrees` | `number` | Compass heading in degrees. `0` = north, `90` = east. |

## Permission

`session.heading.hasPermission` is `true` when `LOCATION` is declared in your
manifest. It reports the manifest declaration, not the OS grant: if the user
denied the system location prompt, `onUpdate()` produces no reading. See
[Permissions](/app-devs/core-concepts/permissions).

<Note>
  `session.heading` works on both Android and iOS. It shares the `LOCATION` manifest
  key with [`session.location`](/app-devs/core-concepts/location).
</Note>