***

id: d1578ee9-90b3-468e-a9aa-2fe587315475
title: detectFax
slug: /node/reference/voice/call/detect-fax
description: detectFax method for the Call class.
max-toc-depth: 3
----------------

[calldetect-events]: /docs/server-sdk/v4/node/reference/voice/call-detect#events

[calldetect-onstarted]: /docs/server-sdk/v4/node/reference/voice/call-detect#onstarted

[calldetect]: /docs/server-sdk/v4/node/reference/voice/call-detect

### detectFax \[#voice\_call\_detect\_fax]

* **detectFax**(`params?`): `Promise`\<[`CallDetect`][calldetect]>

Detects the presence of a fax machine.

#### Parameters

<ParamField path="params" type="object">
  Object containing the parameters for fax detection.
</ParamField>

<Indent>
  <ParamField path="timeout" type="number" default="30.0">
    Number of seconds to run the detector for.
  </ParamField>

  <ParamField path="tone" type="&#x22;CED&#x22; | &#x22;CNG&#x22;" default="CED">
    The fax tone to detect: `CED` or `CNG`.
  </ParamField>

  <ParamField path="waitForBeep" type="boolean" default="false">
    Whether to wait until the device is ready for voicemail delivery.
  </ParamField>

  <ParamField path="listen" type="object">
    Callback to listen for events. List of detect events can be found [here][calldetect-events]. Example event: [`onStarted`][calldetect-onstarted].
  </ParamField>
</Indent>

#### Returns

`Promise`\<[`CallDetect`][calldetect]>

A promise that resolves to a [`CallDetect`][calldetect] object that you can use to
view the current state and results of the `detect` session.

#### Example

```js
import { SignalWire } from "@signalwire/realtime-api";

const client = await SignalWire({ project: "ProjectID Here", token: "Token Here" })

const voiceClient = client.voice;

// Setup a voice client tolisten for incoming calls
await voiceClient.listen({
  topics: ['office'],
  onCallReceived: async (call) => {
    // Answer the call
    console.log("Call received");
    call.answer();
    // Fax detection
    await call.detectFax({
      tone: 'CNG',
      listen: {
        onStarted: () => {
          console.log("Fax detection started");
        },
        onUpdated: (event) => {
          console.log("Fax detection updated:", event.result);
        },
        onEnded: (event) => {
          console.log("Fax detection finished:", event.result);
          call.hangup();
        }
      }
    }).onStarted()
  }
})
```