---
title: activate()
framework: Accessory Transport Extension
role: symbol
role_heading: Instance Method
platforms: [iOS 27.3+]
path: accessorytransportextension/accessoryfeatureruntimesession/activate()
---

# activate()

Registers the session and requests that the system start it.

## Declaration

```swift
func activate() async throws
```

## Mentioned in

Sending data to an accessory in the background

## Discussion

Discussion Returning from this method doesn’t mean the session started. The system calls sessionStarted(_:) after registering the session and after your app enrolls the feature. For more information about feature enrollment, see Accessory features. This method throws AccessoryTransportSession.Error.unavailable if the feature isn’t available on the device, and the system throws an error if a live session for the same feature already exists. This method doesn’t throw when the feature isn’t enrolled for the accessory. Check the status with AccessoryWorker/authorizationStatus(for:) before you call this method.

## See Also

### Managing the session life cycle

- [invalidate()](accessorytransportextension/accessoryfeatureruntimesession/invalidate().md)