F5Bot is a simple service that monitors social media (such as Reddit) for keywords. It emails you when your keywords show up. It's free to use.
I wrote an article about how F5Bot works and how I programmed it. You may find it interesting if you're interested in how web scraping works. In particular, I'm proud that I'm able to scrape and process all of Reddit (posts + comments) in real time, and I'm doing it on one tiny VPS.