Some viewers like to lurk in channels without being seen. I suggest not doing this. Get more info on this at https://twitchtips.com/greeter-bots/
There’s dozens of alerter tools already. If you want something easy to use, check out http://tnotifier.com
There’s dozens of bots that do this already. Learn about chat bots at https://twitchtips.com/chat-moderation-bots/