Save your search criteria and select email alert then pick settings. Every time something new hits the market, price changes,pictures added, goes under contract, etc that match your home search criteria you will receive an email alert.The MLS systems is live and updates every 15 minutes or so. If you like the listings click on the heart to bookmark it for later or call your Realtor to go see it.
If you have not figured out how to up your notifications let me know and i can it for you in 3 minutes tops.
You could use HAR.com to save your search in "my home finder" and be alerted when a home that matches your criteria hits the market, or you could use a Realtor to the same search up. Also, I believe HAR is working on an updated app that may have this capability, but not 100% sure. Hope this helps! V