Not one drive does this on its own. All require the hardware then some software and most if not all the time some action on your part to make the backup happen.

For me I get by with a SYNC APP. There are so many that I can't choose for you from Roadkil's Unstoppable Copier, Syncback, and so many others that sync only the file changes from what folders you specify.

As to the actually HDD I will flatly pan any Seagate. Try the usual Toshiba Canvio. run about 60 to 80 dollars.