Hooking up the voice intercom to Slack

The intercom from the street to our office was connected to an old GSM phone, and letting people in required us to pick up the phone and press the digit 5. Simple, sure, but it doesn’t feel like 2015. I had also been meaning to try the Twilio API for some time.

Task: Connect the Intercom to Slack.

The Twilio API is great, so it was actually really easy to accomplish. I bought a local number and asked our landlord to forward the Intercom to it. Then I set up this simple TwiML script on a web server:

  <Say>Welcome to Earth People. Please stand by.</Say>
  <Enqueue waitUrl="http://x.urtp.pl/slack/service_porttelefon_wait.php"> </Enqueue>

What happens here is that Twilio will pick up the call and greet the intercom user using Twilio’s text to speech service. It will then put the “call” into a new phone queue. Twilio will generate a phone queue id and pass it via POST to the waitUrl, below:

header("content-type: text/xml");
echo "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n";
file_put_contents('input_porttelefon.txt', $_POST['QueueSid']);
# curl post to slack
$data = array(
  "channel" => "#general",
  "username" => "Intercom",
  "text" => "Meep Meep! Open the door with 'Intercom'",
  "icon_emoji" => ":door:"
$url_send = "https://hooks.slack.com/services/xxx/xxx/xxx";
$str_data = json_encode($data);
$ch = curl_init($url_send);
curl_setopt($ch, CURLOPT_CUSTOMREQUEST, "POST");
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_POSTFIELDS, $str_data);

The waitUrl will save the phone queue id to a text file, make an incoming webhook to Slack and of course play a funky tune to the intercom user. Now Twilio will play the funky tune until it ends, or an incoming HTTP-request is made to the Twilio REST API, using the queue id.

Slack is set up to make an outgoing webhook to a URL. This URL just pops the only call in the queue to the front of the queue.

# when incoming hook: read call sid from file and call twilio.
$QueueSid = file_get_contents('input_porttelefon.txt');
  $sid = "xxx";
  $token = "xxx";
  $client = new Services_Twilio($sid, $token);
  $member = $client->account->queues->get($QueueSid)->members->get("Front");
    "Url" => "http://x.urtp.pl/slack/service_porttelefon_dtmf.xml",
    "Method" => "GET"
  file_put_contents('input_porttelefon.txt', '');
  echo '{"text": "Ok, opened."}';
  echo '{"text": "No one is at the door."}';

The last step is to have Twilio play the sound of the digit 5, which opens the door, using the same kind of XML as step 1. Easy!

Next up is to let intercom users, which we don’t let in for some reason, leave a voice message which is posted to Slack. Totally doable, but not we’re quite there yet.