# watch\_src20\_events\_with\_key

Watch SRC20 Transfer and Approval events using an explicit viewing key, without requiring wallet authentication.

## Signatures

```python
def watch_src20_events_with_key(
    w3: Web3,
    *,
    viewing_key: Bytes32,
    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_with_key(
    w3: AsyncWeb3,
    *,
    viewing_key: Bytes32,
    ...same keyword args...
) -> AsyncSRC20EventWatcher
```

## Parameters

| Parameter       | Type                                                                                 | Default    | Description                                          |
| --------------- | ------------------------------------------------------------------------------------ | ---------- | ---------------------------------------------------- |
| `w3`            | `Web3` / `AsyncWeb3`                                                                 |            | Standard Web3 instance (no Seismic namespace needed) |
| `viewing_key`   | [`Bytes32`](https://docs.seismic.systems/clients/python/api-reference/types/bytes32) |            | 32-byte AES-256 viewing key                          |
| `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                                    |
| `poll_interval` | `float`                                                                              | `2.0`      | Seconds between polls                                |
| `from_block`    | `int \| "latest"`                                                                    | `"latest"` | Starting block                                       |

## Returns

[`SRC20EventWatcher`](https://docs.seismic.systems/clients/python/src20/event-watching/src20-event-watcher) (sync) or [`AsyncSRC20EventWatcher`](https://docs.seismic.systems/clients/python/src20/event-watching/async-src20-event-watcher) (async) — already started.

## Example

```python
import os
from web3 import Web3
from seismic_web3 import Bytes32
from seismic_web3.src20 import watch_src20_events_with_key

w3 = Web3(Web3.HTTPProvider("https://gcp-1.seismictest.net/rpc"))
viewing_key = Bytes32(bytes.fromhex(os.environ["VIEWING_KEY"].removeprefix("0x")))

watcher = watch_src20_events_with_key(
    w3,
    viewing_key=viewing_key,
    on_transfer=lambda log: print(f"Transfer: {log.decrypted_amount}"),
)

# Later...
watcher.stop()
```

## Notes

* Does **not** require `EncryptionState` or a wallet private key — only a plain `Web3` instance and the viewing key
* No RPC call to Directory (unlike `watch_src20_events` which fetches the key)
* Useful when you have a shared viewing key or want to avoid the signed read

## See Also

* [watch\_src20\_events](https://docs.seismic.systems/clients/python/src20/event-watching/watch-src20-events) — Watch with automatic key fetch from Directory
* [SRC20EventWatcher](https://docs.seismic.systems/clients/python/src20/event-watching/src20-event-watcher) — Underlying sync watcher class
* [get\_viewing\_key](https://docs.seismic.systems/clients/python/src20/intelligence-providers/get-viewing-key) — Fetch a key to pass here