If you use G Suite for Education or Business and have five minutes to spare then you’ve got everything you need to make a web-based paging system for FREE.
In essence, it’s a doorbell. But one that can reach you wherever you are.
A simple Google Apps Script bot that fetches news from an RSS feed and posts them to a Hangouts Chat room. – thmslprt/hangouts-chat-rss-bot
This one comes via @dersteppen and is a nice little code project to show how you can send messages into Google Hangouts Chat using Google Apps Script. If you are looking for a more secure way of posting into Hangouts Chat the official docs include information on Async messages.
Send push notifications to Hangouts Chat users with Apps Script, do not react only to message sent.
