Detect answering machines

When you call people, a voicemail or a phone menu often answers instead. Answering-machine detection (AMD) listens to the first seconds of the call and tells your application who picked up. Your application decides what to do: talk to the person, leave a message, or hang up. Fonoster never acts on the result for you.

Turn it on

AMD is a setting on the application, off by default. Turn it on for the stream or Autopilot agent that takes your calls.

Dashboard
SDK
CLI

Stream: go to Streams, open the stream, go to the Call handling tab, and turn on Detect answering machines.
Autopilot agent: open the agent, go to the Advanced tab, choose Edit on the Call handling panel, and turn on Detect answering machines.

Choose Save. The dashboard uses the default window of 4 seconds.

Set amd when you create or update the application. An update replaces the whole application, so read it first, change amd, and send all of it back:

const apps = new SDK.Applications(client);
const app = await apps.getApplication("4b01c9b1-8cb1-48fb-bd49-f3daf13463a9");
await apps.updateApplication({
  ...app,
  amd: { enabled: true, windowMs: 4000 }
});

Turn it on with --amd, or set the window with --amd-window, which turns it on too:

fonoster applications:update 4b01c9b1-8cb1-48fb-bd49-f3daf13463a9 --amd-window 4000

--no-amd turns it off.

Field	Default	What it does
`amd.enabled`	`false`	Turns detection on.
`amd.windowMs`	`4000`	How much of the answering side’s speech to listen to, in milliseconds, from `500` to `15000`.

A longer window gives a surer answer, but your application waits longer for it. Voicemail greetings are often long and steady, so the default window is enough for most calls.

Read the result

Once per call, a stream gets an amd.result event:

session.on("amd.result", async ({ status, confidence }) => {
  if (status === "voicemail" || status === "machine") {
    await session.say(
      "Hi, this is Acme Dental calling about your appointment tomorrow. Please call us back at 809 555 0123."
    );
    await session.hangup();
  }
});

The event has these fields:

Field	What it holds
`status`	Who answered: `human`, `voicemail`, `machine`, `ivr` (a phone menu) or `unknown`.
`confidence`	How sure the detector is, from `0` to `1`.
`detector`	The detector that decided, or `none` when detection couldn’t run.
`audioMs`	How many milliseconds of audio it listened to, from when the other side started speaking.
`speechOnsetMs`	How many milliseconds of audio arrived before the other side started speaking. Not set when nobody spoke.
`reason`	Only when `status` is `unknown` because detection couldn’t run, for example `no_speech` when nobody spoke.

The call stays up while detection runs. Your application has the call from the moment it’s answered, so it can speak right away, or wait for the result first.

How long it takes

Detection starts listening when the call is answered and the window starts when the other side begins to speak. The result arrives shortly after the window ends. If nobody speaks within 4 seconds, the result is unknown with the reason no_speech. A person who picks up and stays quiet looks like that too, so treat unknown as “maybe a person”: greet them and listen.

Pick a strategy

Goal	What to do
Leave a message on voicemail	On `voicemail` or `machine`, speak your message and hang up. Voicemail usually records after its beep, so wait a moment or keep the message short.
Only talk to people	On `voicemail`, `machine` or `ivr`, hang up.
Reach a person behind a menu	On `ivr`, send keys with `playDtmf`. See DTMF.
Lowest delay for people	Greet at once, and act on the result only if it’s not `human`.

Use confidence to be careful: for example, hang up on voicemail only when confidence is above 0.8.

Inbound calls and Autopilot agents

AMD runs on every call the application takes, inbound too. It’s most useful on outbound calls. Streams with the twilio protocol don’t get the event, because Twilio Media Streams has no message for it. In Python, listen with session.on("amd.result", handler) the same way. An Autopilot agent doesn’t act on the result: it talks to whoever answers. The result is still saved in the call’s call record, so you can see afterwards how many calls reached voicemail. The amd fields are in Autopilot configuration, and the amd.result event is in the Voice SDK reference.

Next steps

Make outbound calls

Place the calls that AMD checks.

DTMF

Get through phone menus with keypad tones.

Build a stream with the Voice SDK

Handle the result in your own code.

Call records

Find the AMD result of past calls.

Get started

Autopilot

Streams

Telephony

Observe

Workspace

Reference

Self-hosting

Private regions

Hacking Fonoster

Detect answering machines

Turn it on

Read the result

How long it takes

Pick a strategy

Inbound calls and Autopilot agents

Next steps

Make outbound calls

DTMF

Build a stream with the Voice SDK

Call records

​Turn it on

​Read the result

​How long it takes

​Pick a strategy

​Inbound calls and Autopilot agents

​Next steps

Make outbound calls

DTMF

Build a stream with the Voice SDK

Call records

Turn it on

Read the result

How long it takes

Pick a strategy

Inbound calls and Autopilot agents

Next steps