Implement Answering Machine Detection with Ruby & Sinatra

This guide utilizes the Answering Machine Detection feature to determine whether a human or voicemail machine has answered the call. This allows your program to determine whether to dial a number to connect someone to the human or leave a message for the voicemail box.

When a call is initiated with machine_detection set to DetectMessageEnd, there is a parameter posted to the webhook called AnsweredBy. The potential options here are machine_end_other, machine_end_beep, machine_end_silence, and human. If the parameter returned is anything other than human, this example will take a short pause to wait for the beep and then play a message for the intended recipient. If the parameter returned is human, it will dial a number to connect the human to another person.

Configuring the Code

We start by creating a route for Sinatra and initializing response as a VoiceResponse object, which is required in order to use Say, Dial, Hangup, and Pause.

post '/start' do
  response =

Now we use a switch statement to designate that we will take different actions depending on the value of [:AnsweredBy]. You can see below that if anything other than human is returned, this code will output "It's a machine", take a brief pause to allow the voicemail system time to reach the recording beep, leave a voicemail for the intended recipient, and hang up. If the value returned is human, this code will output "We got ourselves a live human here!" and then dial the number of your agent (or the next part of your standard call flow). In the dial, you have the option to either hard code the number you would like to dial or use environment variables.

case params[:AnsweredBy]
  when 'machine_end_other', 'machine_end_silence', 'machine_end_beep'
    puts "It's a machine!"
    # put in a little pause to allow the recording to start on the other end
    response.pause(length: 1)
    # replace messsage with whatever voicemail you want to leave
    response.say(message: "Hello! This is the County Medical Center. We are calling you to confirm your doctor appointment. Please call us back as soon as possible.")
  when 'human'
    puts "We got ourselves a live human here!"
    response.dial do |dial|
      # defaulting to calling a time voice announcement number as an example
      dial.number(ENV.fetch('AGENT_NUMBER', '+12027621401'))

When [:AnsweredBy] returns any value other than human, the XML code is a simple <Say>.

<?xml version="1.0" encoding="UTF-8"?>
<Say>Hello! This is the County Medical Center. We are calling you to confirm your doctor appointment. Please call us back as soon as possible.</Say>

When [:AnsweredBy] returns human, the XML code consists of a <Dial>.

<?xml version="1.0" encoding="UTF-8"?>

Triggering calls

There are a number of different ways that you could trigger your outbound call, but here are two examples using Ruby and cURL. The most important takeaway from these is that no matter how you initiate your call, you must have machine_detection set to DetectMessageEnd. There is another parameter option enable, but that will not work in the same way. The parameter enable would work if you wanted to do some action for a human and hang up if the answering party is a machine, however, it will not allow you to take specific actions in both scenarios.

You will need your SignalWire Project ID, auth token, and space URL. You can easily find all three values in a copyable format in your SignalWire Dashboard by clicking the API tab on the lefthand sidebar.

As the above code is written in Ruby, you can always stay consistent and initiate the call using the SignalWire Ruby SDK. You can either set environment variables on your computer, or you can replace the ENV variables with your Project ID, auth token, and space URL.


  call = client.calls.create(
    url: ENV['APP_DOMAIN'] + '/start',
    to: params[:to],
    from: ENV['FROM_NUMBER'],
    machine_detection: "DetectMessageEnd"

You can also use cURL on your command prompt or with a tool such as postman to send HTTP requests to create the call. You will need to replace the ProjectID and Space URL within the cURL URL, as well as the webhook pointing to this code, the To number, the From number, and the authentication at the bottom.

curl \
  -X POST \
  --data-urlencode "Url=YOUR-WEBHOOK-URL" \
  --data-urlencode "To=DESTINATION-NUMBER" \
  --data-urlencode "From=CALLER-ID-FROM-SIGNALWIRE-ACCOUNT" \
  --data-urlencode 'MachineDetection=DetectMessageEnd' \

Docker instructions

Copy env.example to .env and edit the file, adding the necessary SignalWire credentials and other phone numbers you will need.

Build the image with docker build . -t rubyamd, then run the script using docker run -it --rm -p 8080:8080 --name rubyamd --env-file .env rubyamd.

Sign Up Here

If you would like to test this example out, you can create a SignalWire account and space here.

Please feel free to reach out to us on our Community Slack or create a Support ticket if you need guidance!

What’s Next

Check out the full code on our SignalWire Github Repo!

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