> For the complete documentation index, see [llms.txt](https://docs.seismic.systems/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.seismic.systems/clients/python/src20/event-watching/watch-src20-events.md).

# watch\_src20\_events

Watch SRC20 Transfer and Approval events for your wallet, automatically fetching your viewing key from the Directory contract via signed read.

## Signatures

```python
def watch_src20_events(
    w3: Web3,
    *,
    encryption: EncryptionState,
    private_key: PrivateKey,
    token_address: ChecksumAddress | None = None,
    on_transfer: TransferCallback | None = None,
    on_approval: ApprovalCallback | None = None,
    on_error: ErrorCallback | None = None,
    poll_interval: float = 2.0,
    from_block: int | str = "latest",
) -> SRC20EventWatcher

async def async_watch_src20_events(
    w3: AsyncWeb3,
    *,
    encryption: EncryptionState,
    private_key: PrivateKey,
    ...same keyword args...
) -> AsyncSRC20EventWatcher
```

## Parameters

| Parameter       | Type                                                               | Default    | Description                                    |
| --------------- | ------------------------------------------------------------------ | ---------- | ---------------------------------------------- |
| `w3`            | `Web3` / `AsyncWeb3`                                               |            | Web3 instance with Seismic support             |
| `encryption`    | [`EncryptionState`](/clients/python/client/encryption-state.md)    |            | Encryption state from wallet client            |
| `private_key`   | [`PrivateKey`](/clients/python/api-reference/types/private-key.md) |            | Signing key for Directory signed read          |
| `token_address` | `ChecksumAddress \| None`                                          | `None`     | SRC20 contract to filter (`None` = all tokens) |
| `on_transfer`   | Callback                                                           | `None`     | Invoked for Transfer events                    |
| `on_approval`   | Callback                                                           | `None`     | Invoked for Approval events                    |
| `on_error`      | Callback                                                           | `None`     | Invoked on errors (decryption, RPC)            |
| `poll_interval` | `float`                                                            | `2.0`      | Seconds between polls                          |
| `from_block`    | `int \| "latest"`                                                  | `"latest"` | Starting block                                 |

## Returns

[`SRC20EventWatcher`](/clients/python/src20/event-watching/src20-event-watcher.md) (sync) or [`AsyncSRC20EventWatcher`](/clients/python/src20/event-watching/async-src20-event-watcher.md) (async) — already started.

## Example

```python
import os
from seismic_web3 import PrivateKey, SEISMIC_TESTNET
from seismic_web3.src20 import watch_src20_events

pk = PrivateKey.from_hex_str(os.environ["PRIVATE_KEY"])
w3 = SEISMIC_TESTNET.wallet_client(pk)

with watch_src20_events(
    w3,
    encryption=w3.seismic.encryption,
    private_key=pk,
    on_transfer=lambda log: print(f"Transfer: {log.decrypted_amount}"),
) as watcher:
    input("Press Enter to stop...\n")
```

## Notes

* Fetches your viewing key from Directory via `get_viewing_key()` on creation — raises `ValueError` if no key registered
* The watcher starts automatically; call `.stop()` or use context manager to clean up
* If you already have the viewing key, use [`watch_src20_events_with_key()`](/clients/python/src20/intelligence-providers/watch-src20-events-with-key.md) to skip the signed read

## See Also

* [watch\_src20\_events\_with\_key](/clients/python/src20/intelligence-providers/watch-src20-events-with-key.md) — Watch with explicit key (no wallet needed)
* [SRC20EventWatcher](/clients/python/src20/event-watching/src20-event-watcher.md) — Underlying sync watcher class
* [register\_viewing\_key](/clients/python/src20/intelligence-providers/register-viewing-key.md) — Register a key first


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