***

title: Call Control
sidebarTitle: Call Control
description: End calls and transfer to humans from within your agent.
---------------------------------------------------------------------

Control the call flow from within your agent. End calls gracefully or transfer to a human.

## Ending Calls

Use `SDKAgentEndCallEvent` to end the call:

```python
from smallestai.atoms.agent.nodes import OutputAgentNode
from smallestai.atoms.agent.events import SDKAgentEndCallEvent
from smallestai.atoms.agent.tools import function_tool

class MyAgent(OutputAgentNode):
    @function_tool()
    async def end_call(self) -> None:
        """End the call gracefully."""
        await self.send_event(SDKAgentEndCallEvent())
        return None
```

<Note>
  Tools that send SDK events must use `await self.send_event()` and return `None`. Simply returning the event object won't work.
</Note>

## Transferring to Humans

Use `SDKAgentTransferConversationEvent` to hand off to a human:

```python
from smallestai.atoms.agent.events import (
    SDKAgentTransferConversationEvent,
    TransferOption,
    TransferOptionType
)
from smallestai.atoms.agent.tools import function_tool

class MyAgent(OutputAgentNode):
    @function_tool()
    async def transfer_to_human(self) -> None:
        """Transfer to a human agent."""
        await self.send_event(
            SDKAgentTransferConversationEvent(
            transfer_call_number="+14155551234",
            transfer_options=TransferOption(
                type=TransferOptionType.COLD_TRANSFER
            ),
            on_hold_music="relaxing_sound"
        )
        )
        return None
```

### Transfer Parameters

| Parameter              | Type           | Required | Description                                                        |
| ---------------------- | -------------- | -------- | ------------------------------------------------------------------ |
| `transfer_call_number` | string         | Yes      | Human agent's phone (E.164)                                        |
| `transfer_options`     | TransferOption | Yes      | Transfer type                                                      |
| `on_hold_music`        | string         | No       | `"ringtone"`, `"relaxing_sound"`, `"uplifting_beats"`, or `"none"` |

### Transfer Types

```python
from smallestai.atoms.agent.events import (
    TransferOption,
    TransferOptionType,
    WarmTransferPrivateHandoffOption,
    WarmTransferHandoffOptionType,
)

# Cold transfer (immediate handoff)
cold = TransferOption(type=TransferOptionType.COLD_TRANSFER)

# Warm transfer (agent briefs human first)
warm = TransferOption(
    type=TransferOptionType.WARM_TRANSFER,
    private_handoff_option=WarmTransferPrivateHandoffOption(
        type=WarmTransferHandoffOptionType.PROMPT,
        prompt="Customer calling about billing"
    )
)
```

## Call Flow Events

When these events trigger, they appear in call logs:

| Event                               | Log Entry                 |
| ----------------------------------- | ------------------------- |
| `SDKAgentEndCallEvent`              | `hangupSource: "agent"`   |
| `SDKAgentTransferConversationEvent` | `transferTarget: "+1..."` |

## Tips

<AccordionGroup>
  <Accordion title="Announce transfers">
    Tell the user before transferring: "I'll connect you to..."
  </Accordion>

  <Accordion title="Use cold transfer for simple handoffs">
    Faster than warm transfers.
  </Accordion>

  <Accordion title="Graceful endings">
    Say goodbye before ending, don't just hang up.
  </Accordion>

  <Accordion title="Fallback numbers">
    Have a general transfer number if specific departments unavailable.
  </Accordion>
</AccordionGroup>