# Event Source ID

Return a code representing the origin of the event on the bus (button, pin, radio, and so on).

```sig
control.eventSourceId(EventBusSource.MICROBIT_ID_BUTTON_A);
```

**This is an advanced API.**  For more information, see the
[micro:bit runtime messageBus documentation](https://lancaster-university.github.io/microbit-docs/ubit/messageBus/)
