Recommended hard drive monitoring (Ubuntu server) options?

I've had a home server for years, at first using Windows Server, then Unraid, and now using Ubuntu server. I've long known that I should keep a close eye on my spinning rust, but I never really knew the best way to have that monitoring quietly automated in the background, only sending me a message when something bad shows up. If it matters at all (I assume it doesn't) I am using ZFS on Ubuntu (but not using ZFS as root. It's mounted in e.g ~/user/storage. My primary drive is an SSD)

What are you all using for hard drive monitoring? What are you using for notifications and (generally) how are you linking those two together?