Get an update on console as soon as a slot opens up in https://selfregistration.cowin.gov.in/ . Login to the website and then run this script on Console.

cowin_schedule_v3.js

// This script will alert you whenever some slot opens up on the given date within the given pincodes
// Change the pincodes to your needs as per your city
// Optionally: the next_days variable can be set to number of days it has to check. (If you set to 3, will check for next three days.)

// How To setup Video -> https://www.youtube.com/watch?v=3_N5FFegtI4

// Steps to use
// 1. Update Config
// 2. Login to https://selfregistration.cowin.gov.in/
// 3. Rigt Click on the website
// 4. Click on Inspect
// 5. Open the Console Tab on your Inspect window
// 6. Copy paste the contents of this entire file - cowin_schedule_v2.js
// 7. Press Enter
// It will run every 15 seconds and check for availability of slots.

// Config
// ------

var pincodes = ["560078", "560076", "560020", "560011"];
var next_days = 3;

var date = new Date();
var dateArr = [];

for ( x=0; x < next_days; x++)
{
  date.setDate(date.getDate() + 1);//Start from tomorrow (skip today)
  var d = date.getDate();
  var m = date.getMonth() + 1;
  var y = date.getFullYear();
  var dateString = (d <= 9 ? '0' + d : d) + '-' + (m <= 9 ? '0' + m : m) + '-' + y;
  dateArr.push(dateString);
}

var trialCounter = 1;

const sleepNow = (delay) => new Promise((resolve) => setTimeout(resolve, delay))

function httpGet(theUrl)
{
    var xmlHttp = new XMLHttpRequest();
    xmlHttp.open( "GET", theUrl, false ); // false for synchronous request
    xmlHttp.send( null );
    return xmlHttp.responseText;
}

async function fetchByPincode() {
    console.log("Check: ", trialCounter++);

    for (i=0;i < pincodes.length; i++) {
      for (j=0; j < dateArr.length; j++) {
        url = "https://cdn-api.co-vin.in/api/v2/appointment/sessions/calendarByPin?pincode="+pincodes[i]+"&date="+dateArr[j];
        await sleepNow(1100);
        a = httpGet(url);
        try {
          a = JSON.parse(a)
        } catch(e) {
          continue;
        }
        for (c in a.centers) {
        for (s in a.centers[c].sessions) {
              if (a.centers[c].sessions[s].min_age_limit < 45 && a.centers[c].sessions[s].available_capacity > 0) {
                console.log("Try Booking for: ", a.centers[c].pincode, a.centers[c].name, a.centers[c].sessions[s].available_capacity);
                console.log("Date: "+dateArr[j])
                var audio = new Audio('https://media.geeksforgeeks.org/wp-content/uploads/20190531135120/beep.mp3');
                audio.play();
              }
              else {
                console.log("no slots available for "+pincodes[i]+" on "+dateArr[j]);
              }
          }
        }
      }
    }
    await sleepNow(15000);
    fetchByPincode();
}

console.log('Script Initialising');
fetchByPincode();