Swizec Teller - a geek with a hatswizec.com

Senior Mindset Book

Get promoted, earn a bigger salary, work for top companies

Senior Engineer Mindset cover
Learn more

    Livecoding #22: A door-answering Slackbot

    This is a Livecoding Recap – an almost-weekly post about interesting things discovered while livecoding ?. Always under 500 words and with pictures. You can follow my channel, here. New streams almost every Sunday at 2pm PDT. There’s live chat, come say hai ?

    Aaaaaalmost hacked together a Slack bot that can answer the door. There’s one last step to figure out and then we are ready to rock. ??

    Buildings in the US, or at least in San Francisco, have buzzers that connect to a phone rather than a purpose-built wall-mounted device. You set it up with your phone, and whenever someone wants to come visit, your phone rings, you say Hello, and buzz them in.

    It’s perfect for the home. It’s really annoying for anyone stuck with buzzer duty at the office.

    A Slack bot can do that for us. Here’s the idea:

    • give the buzzer a Twilio phone number
    • build a small node.js server to answer the phone
    • send Slack message with an “I am so and so” audio clip
    • offer Deny and Let them in buttons
    • anyone can buzz anyone in
    • profit.

    The profit part comes if Slack lets me release this as a, say, $10/month service. We’ll see. ?

    You can also play with it as an open source project on Github. But it’s not really ready for prime-time yet. The code is a mess, and there’s no README file to tell you how to set it up.

    The bright side is that you can see all my API keys in the livecoding video. I’m going to change those. Probably.

    When Twilio receives a phone call, it posts to our webhook on <server>/call. This is the start of our user experience. We reply with Hello! State your name, then press anything. Like this:

    router.post("/call", function (req, res, next) {
      const caller = req.body.Caller;
      const callSid = req.body.CallSid;
      let twiml = new twilio.TwimlResponse();
      twiml.say("Hello! State your name, then press any key.", { voice: "alice" });
        action: `/call/recording/${callSid}`,
        //transcribe: true,
        //transcribeCallback: `/call/recording/${callSid}`,
        maxLength: 60,

    That twiml stuff constructs a response using TwiML, a Twilio-extended XML language. Twilio can turn <Say>text</Say> commands into spoken dialogue using various voice synthesizers. You’ve gotta use proper punctuation though. It sounds weird otherwise.

    We ask Twilio to record a response and send the audio clip to our /call/recording/<id> API. In that API, we send a Slack text and put the caller on hold.

    router.post("/call/recording/:callSid", (req, res, next) => {
      const callSid = req.params.callSid;
      const twiml = new twilio.TwimlResponse();
      const recordingUrl = req.body.RecordingUrl;
      let data = {
        attachments: [
            fallback: "Somebody is at the door",
            title: "Somebody is at the door",
            title_link: recordingUrl,
            text: "Click link to hear the recording",
            callback_id: `door_open:${callSid}`,
            actions: [
                name: "open_door",
                text: "Let them in",
                type: "button",
                value: "open_door",
                name: "deny_access",
                text: "No.",
                type: "button",
                value: "deny_access",
      webSlack.chat.postMessage("#bot-testing", "", data, () => {
        twiml.say("Thank you. Please hold.", { voice: "alice" });

    We get the audio clip as a URL, and we post to Slack using their Web client thingy. The real-time-messaging client can’t do complex messages.

    This is what you get on Slack:


    Now comes the part I haven’t figured out yet:

    1. Build the API for those Slack buttons – it always throws an error ?
    2. Figure out how to continue sending to a Twilio call outside of the original webhoook, if I know the original call ID.

    The first bit is just a matter of figuring out my config. Slack gives clear instructions for doing that; I just gave up too soon.

    The second bit, though… that’s hard. I can’t find any documentation for it, and I haven’t had any luck Googling for it either.

    Gonna talk to Twilio’s help team and finish this up next Sunday. Don’t forget to come watch.

    Published on September 19th, 2016 in Livecoding, Startups, Technical

    Did you enjoy this article?

    Continue reading about Livecoding #22: A door-answering Slackbot

    Semantically similar articles hand-picked by GPT-4

    Senior Mindset Book

    Get promoted, earn a bigger salary, work for top companies

    Learn more

    Have a burning question that you think I can answer? Hit me up on twitter and I'll do my best.

    Who am I and who do I help? I'm Swizec Teller and I turn coders into engineers with "Raw and honest from the heart!" writing. No bullshit. Real insights into the career and skills of a modern software engineer.

    Want to become a true senior engineer? Take ownership, have autonomy, and be a force multiplier on your team. The Senior Engineer Mindset ebook can help 👉 swizec.com/senior-mindset. These are the shifts in mindset that unlocked my career.

    Curious about Serverless and the modern backend? Check out Serverless Handbook, for frontend engineers 👉 ServerlessHandbook.dev

    Want to Stop copy pasting D3 examples and create data visualizations of your own? Learn how to build scalable dataviz React components your whole team can understand with React for Data Visualization

    Want to get my best emails on JavaScript, React, Serverless, Fullstack Web, or Indie Hacking? Check out swizec.com/collections

    Did someone amazing share this letter with you? Wonderful! You can sign up for my weekly letters for software engineers on their path to greatness, here: swizec.com/blog

    Want to brush up on your modern JavaScript syntax? Check out my interactive cheatsheet: es6cheatsheet.com

    By the way, just in case no one has told you it yet today: I love and appreciate you for who you are ❤️

    Created by Swizec with ❤️